Add slow query parse logging

[frodsan]

• Adds log_min_duration_parse (ms) config option: when set, emits a WARN log for any query whose parse time meets or exceeds the threshold.
• Adds log_query_sample_length (default: 100) to cap how many characters of the query are included in the log line, keeping logs readable for long queries.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 84.09091% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/frontend/router/parser/cache/ast.rs	30.00%	7 Missing ⚠️

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