feat: omnisharded > sharded in config

[levkk]

Make omnisharded tables config take priority over sharded config. If config says a table is omnisharded, and it has the sharding key anyway, PgDog will treat it as omnisharded.

[codecov]

Codecov Report

❌ Patch coverage is 99.35484% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...frontend/router/parser/query/test/test_sharding.rs	95.45%	1 Missing ⚠️

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