feat(cdc): allow decimal to rw_int256 and varchar

[KeXiangWang]

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What's changed and what's your intention?

Resolve #15977. With this PR, numeric in PG can be converted into rw_int256 or varchar implicitly through CDC.
The only thing user need to do is when create table, mark the data type of the column corresponding to numeric as rw_int256 or varchar.

One thing worth mentioning is that the numerics with decimal parts will be considered as NULL if the column is to be converted to rw_int256.

Currently, it's only for postgres. We can add support for mysql later if requested.

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[lmatz]

LGTM, thanks!

[KeXiangWang]

Also kindly mention @bestmike007

[xiangjinwu]

Supposed to be NaN and Infinity?

[KeXiangWang]

Yes. Trying to resolve this issue. If it's too non-trivial, I'll open another PR to fix it. Besides, I also find that in our shared source cdc, the conversion from pg-numeric to rw-numeric will also lose Infinity and -Infinity. Will fix it soon.

[KeXiangWang]

🫠Too complicated to fix, as it requires us to know the types in upstream tables when parsing the data in JSON payload. Otherwise, we cannot distinguish whether a string is converted from a numeric or a real varchar.

So in this PR, when mapping pg-numeric to varchar, NaN will be NAN, inf will be POSITIVE_INFINITY , and -inf will be NEGATIVE_INFINITY . At least these behavior is aligned among backfiling and normal data updates. Do you think that's acceptable?

For the bug in the conversion from pg-numeric to rw-numeric, I'll create a PR later to resolve it.

[KeXiangWang]

Create a issue here to record.

[StrikeW]

LGTM