feat: Enable simple schema evolution for Change Data Feed

[OussamaSaoudi-db]

What changes are proposed in this pull request?

This PR enabled simple forms of schema evolution to change data feed. The supported schema changes are:

• Converting of a column from non-nullable to nullable
• Adding a new nullable column

This PR also removes several unnecessary uses of allow(unused).

How was this change tested?

Updated existing tests to check that performing schema evolution check fails in these cases:

• schema with extra column cannot be read with schema not containing that row
• Column with wider type cannot be read with narrower type in schema
• Type widening is not supported (as of this PR)
• incompatible data types fail
• schema with non-nullable column can be read with schema containing the nullable column
• can read schema with an extra nullable column

The updates to the tests also control more variables so that we test only one thing at a time.

[codecov]

Codecov Report

Attention: Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.07%. Comparing base (6751838) to head (e2a624c).

Files with missing lines	Patch %	Lines
kernel/src/table_changes/log_replay/tests.rs	97.14%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #625      +/-   ##
==========================================
- Coverage   84.08%   84.07%   -0.02%     
==========================================
  Files          76       76              
  Lines       17526    17540      +14     
  Branches    17526    17540      +14     
==========================================
+ Hits        14736    14746      +10     
- Misses       2077     2079       +2     
- Partials      713      715       +2     

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