feat: Remove query comments to improve cache hit rate

[dev-lew]

This PR addresses #560

It modifies the comment function (now parse_comment), which will capture a role and shard and then return the original query string with all comments removed except for those that match 0 or more regexes.

If there is a cache miss, we do another cache lookup after removing comments except for those used for pgdog metadata (pgdog_shard, etc) in the hope that we can increase cache hit rate.

Two associated helper functions were added as well.

Also, some tests were modified to reflect the new functionality.

[codecov]

Codecov Report

❌ Patch coverage is 94.76744% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...dog/src/frontend/router/parser/cache/cache_impl.rs	78.26%	5 Missing ⚠️
pgdog/src/frontend/router/parser/comment.rs	96.72%	4 Missing ⚠️

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