feat: cross-shard OFFSET

[levkk]

Adds support for LIMIT x OFFSET y for cross-shard queries. This rewrites the statement to LIMIT x + y and applies the offset to the result in-memory.

Follow up on #757

[codecov]

Codecov Report

❌ Patch coverage is 95.89744% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...frontend/router/parser/rewrite/statement/offset.rs	94.47%	18 Missing ⚠️
...rontend/client/query_engine/test/rewrite_offset.rs	96.95%	5 Missing ⚠️
pgdog/src/net/messages/bind.rs	94.11%	1 Missing ⚠️

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