Ensure `Value_Type.Byte` behaves consistently between in-memory and Database

[radeusgd]

We have a Value_Type.Byte which is a special type used to represent small 8-bit integers.

Most database systems will treat such type as an unsigned byte with the range of values being 0-255. However, our in-memory backend currently relies on Java's defaults where all numeric types are signed and the byte values are actually -128 to 127. This is not consistent with databases.

• [ ] We should modify our implementation to ensure that Value_Type.Byte actually represents the 0-255 range.
  • With the current non-compact storage that only means amending the bounds. In the future, if we will want a more compact storage, we may need to ensure a proper mapping when storing/retrieving the values (so that we can store them as 8-bit byte type but that Enso will see it as Integer in range 0-255).
• [ ] We should ensure that when fetching a Byte column from a Database or uploading a Byte column to Database all values are mapped correctly.
• [ ] We should ensure that the documentation for Value_Type.Byte defines how it is supposed to behave (e.g. 0-255 regardless of backend/platform).

[radeusgd]

I think this task is kind of blocked by waiting for new database integrations.

That is because our current two backends do not really support a Byte type:

• SQLite just stores integers without limits, so we map everything to Integer 64-bit.
• Postgres does not have a numeric byte type, only a byte array.

So I think it will only matter once we actually have a Database that can store 8-bit integers, e.g. SQL Server that has tinyint.

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It may make sense to tackle the task earlier to ensure we don't introduce a breaking change later (changing the range on Value_Type.Byte from current -128 to 127 to 0-255), though.

[radeusgd]

Just changing the 'working range' should actually be trivial with the current implementation that stores everything as a long. It can easily be done in probably less than half a day. So we may consider doing this change right away and then doing a separate integration once we have a Byte supporting DB backend.

[jdunkerley]

Need to review that round trip is possible.

Should get the value from a byte column as a 0-255 (stored as a long behind the scenes). Need to be able to write back to same DB tech with same type.

[jdunkerley]

It is on hold as no backend currently supported which has a byte type.