feat(kernel): add client query timeout

[cathleeny]

Summary

• Add connector-only WithClientQueryTimeout for the SEA/kernel backend.
• Positive values use kernel_statement_execute_with_timeout_ms; zero and maximum time.Duration are unlimited.
• Bound execution through terminal-state mapping, excluding result materialization/fetching. WithTimeout remains the independent server-side Thrift option.
• Keep context-cancel cleanup from extending an explicit client deadline while preserving the legacy execute cleanup contract.

Depends on databricks-sql-kernel#339 at ec639bd48e84c64d708a0b70a532e44ecf83ad7c; updated kernel bindings are required before release.

Validation

• Kernel-tagged suite and race test against the exact PR 339 archive
• Live E2E: returned non-retryable HYT00 in 5.002s, then successfully reused the same sql.Conn for SELECT 1

[peco-review-bot]

Verdict: 1 Medium

Looks solid — thorough tests and documentation for the new WithClientQueryTimeout kernel option; config plumbing, DeepCopy, sentinel wiring, and the C-ABI max constant are all correct and covered. One medium concurrency concern: the detached-watcher path inverts the legacy canceller-before-statement teardown ordering, whose safety rests on a kernel contract not verifiable from this repo.