add decimal test cases for CDC sources

[lmatz]

some database supports a very large decimal type, i.e. larger than 38-digit decimal which is the typical practice in modern databases.

RW supports an even smaller decimal type, i.e. 28-digit decimal.

We want to make sure the behavior of CDCing these large numbers, i.e. the number is large or the number of digits after decimal point is large or both, into RW is tracked.

[github-actions]

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