Implement the type safety utilities for plugin authors

[illright]

• [x] Make sure all config type definitions (Config, ConfigObject, Plugin, Severity) are exported
• [x] Make sure that the FSD plugin uses them to export a strongly typed object
• [x] Implement everything in import { createPlugin, enableAllRules, type ConfigObjectOf } from '@steiger/toolkit'
• [x] Implement createConfigs similarly to createPlugin

---

Test cases:

• [x] An end-user of the linter should be able to import the FSD plugin and the FSDConfigObject and use satisfies to gain autocompletion for the available rules
• [x] An end-user can quickly create a custom plugin using the createPlugin function to get auto-completion for plugin fields and obtain a highly typed plugin object in the end
• [x] An end-user can define an object of configs containing the all and a hand-picked custom config with the createConfigs function and get auto-completion on the rule names
• [x] A plugin writer can use the ConfigObjectOf to export a type object for their plugin

[illright]

Code for the test case:

import fsd, { type FSDConfigObject } from '@feature-sliced/steiger-plugin'
import { createConfigs, createPlugin, enableAllRules, type ConfigObjectOf } from '@steiger/toolkit'

const sda = createPlugin({
  meta: {
    name: 'sda',
    version: '1.0.0',
  },
  ruleDefinitions: [
    {
      name: "a-rule",
      check(root, ruleOptions: { foo?: "bar" | "baz" }) {
        return {
          diagnostics: [],
        }
      },
    }
  ]
})

const sdaConfigs = createConfigs({
  all: enableAllRules(sda),
  handpicked: [
    sda,
    {
      rules: {
        "a-rule": "off"
      },
    }
  ]
})

export default [
  ...fsd.configs.recommended,
  {
    rules: {
      "fsd/no-public-api-sidestep": "off",
    }
  } satisfies FSDConfigObject,
  sda,
  ...sdaConfigs.handpicked,
  {
    rules: {
      "a-rule": ["error", { foo: "baz" }]
    }
  } satisfies ConfigObjectOf<typeof sda>
]