235 add typing support to event model

[evalott100]

Closes #235

Adds TypedDicts and code to generate schemas from TypedDicts. It's necessary to merge #245 prior to this so black formatting doesn't cause problems.

[evalott100]

@coretl Refactored and added comments, ready for another review!

[evalott100]

Itemising the differences in the schema here

General changes

• Capitalised definition names, is probably nicer since they are linked classes in the typeddicts. They are datatypes in the schema so this doesn't make a difference to operation. https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_start.json#L5-L14

   "definitions": {
      "Calculation": {
         "title": "Calculation",
         "type": "object",
         "properties": {
            "args": {
               "title": "Args",
               "type": "array",
               "items": {}
            },

• Properties now have a title field. No way to remove in pydantic. Could remove manually in the generated json, though these don't matter for operation.

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_start.json#L228

         "properties": {
            "configuration": {
               "title": "Configuration",
               "description": "Static information about projection",
               "type": "object"
            },

• When a datatype $ref is used there is always an allOf block. This doesn't matter since there is only one $ref inside (pydantic forces this behaviour).

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/datum_page.json#L18-L23

         "allOf": [
            {
               "$ref": "#/definitions/Dataframe"
            }
         ]
      },

• default "type": "array" keys where datatype isn't specified now have

          "type": "array",
          "items": {}` 

datum_page.json changes

• The title field in the datum_page.json has changed from title: "datum" to title: "datum_page".

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/datum_page.json#L2

• The dataframe reference in datum_page changed from an array to an array of strings

   "Dataframe": {
       "title": "Dataframe",
       "type": "array",
       "items": {
          "type": "string"
       }

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/datum_page.json#L6-L11

• datum_id is now a Dataframe (still an array of strings). datum_kwargs is now an array, string, bool, or number: https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/datum_page.json#L24-L41

      "datum_kwargs": {
         "title": "Datum Kwargs",
         "description": "Array of arguments to pass to the Handler to retrieve one quanta of data",
         "type": "object",
         "additionalProperties": {
            "anyOf": [
               {
                  "type": "boolean"
               },
               {
                  "type": "string"
               },
               {
                  "type": "number"
               },
               {
                  "type": "array",
                  "items": {}
               }
            ]
         }
      },

• resource is not NotRequired https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/datum_page.json#L52-L55

  "required": [
    "datum_id",
    "resource"
  ],

event.json changes

• filled is now of type

       "type": "object",
       "additionalProperties": {
          "anyOf": [
             {
                "type": "boolean"
             },
             {
                "type": "string"
             }
          ]
       }
    },

  instead of type

  "type": [
             "boolean",
             "string"
          ]

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/event.json#L19-L30

event_descriptor.json

• Introduction of a precision field

      "precision": {
             "title": "Precision",
             "description": "Number of digits after decimal place if a floating point number",
             "type": "integer"
          },

  https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/event_descriptor.json#L66-L69

and units

            "units": {
               "title": "Units",
               "description": "Engineering units of the value",
               "type": "string"
            }

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/event_descriptor.json#L84-L88

event_page.json changes

• DataframeForFilled now has

             "anyOf": [
                {
                   "type": "boolean"
                },
                {
                   "type": "string"
                }
             ]

  instead of

            "type": "array",
            "items": {
               "type": [
                  "boolean",
                  "string"
               ]

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/event_page.json#L20-L27

run_start.json changes

• Calculation now has a reference

   "definitions": {
      "Calculation": {
         "title": "Calculation",
         "type": "object",
         "properties": {
            "args": {
               "title": "Args",
               "type": "array",
               "items": {}
            },

https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_start.json#L5-L6

• projection no longer has a superfluous "." in pattern properties

             "patternProperties": {
                ".": {
                   "$ref": "#/definitions/projection"
                }

  is now

            "additionalProperties": {
                "$ref": "#/definitions/Projection"
             }

• Hints now has its own reference https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_start.json#L33

• sample is now of type

       "anyOf": [
          {
             "type": "object"
          },
          {
             "type": "string"
          }

  instead of type

       "type": [
          "object",
          "string"
       ]

  https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_start.json#L308-L314

run_stop.json changes

• data_type no longer has unnecessary second "^([^./]+)$" pattern property, it's already done here

  "patternProperties": {
    "^([^./]+)$": {
       "$ref": "#/definitions/DataType"
    }

• Blank "properties": {}, removed from num_events https://github.com/evalott100/event-model/blob/e91f648dc74c294a97ceac497f25cb6d6d193d87/event_model/schemas/run_stop.json#L30-L36