transaction: Handle commit_ts expired error

[pingyu]

Cherry pick #491

Changes

• Add retry loop for KeyError::commit_ts_expired when committing the primary key, mirroring client-go’s actionCommit::handleSingleBatch logic (src/transaction/transaction.rs).
• Improve error visibility/logging for primary commit failures and key mismatch (uses HexRepr) (src/transaction/transaction.rs, src/kv/mod.rs).
• Fix HasKeyErrors for Result<T, Error> to preserve structured errors (especially MultipleKeyErrors) instead of stringifying, enabling correct extraction/matching (src/store/errors.rs).
• Improve test helper error message when PD HTTP response body isn’t valid JSON (tests/common/ctl.rs).

Compare with Go implementation (https://github.com/tikv/client-go/blob/tidb-8.5/txnkv/transaction/commit.go) by LLM:

• commit_ts_expired handling: Committer::commit_primary_with_retry in src/transaction/transaction.rs:1408 matches actionCommit::handleSingleBatch’s CommitTsExpired branch—logs, verifies the rejected key is the
  primary (:1419-1424), rejects “too large min_commit_ts” (:1426-1436), and retries (:1437). Rust retries by re-running commit_primary() which re-fetches a fresh TSO and rebuilds the commit request (:1372-1406),
  which is equivalent to Go’s “update commitTS + update request + continue”.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: coocood, iosmanthus

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-20 12:25:58.444855303 +0000 UTC m=+496786.058812159: ☑️ agreed by coocood.
• 2026-01-20 12:28:59.215054551 +0000 UTC m=+496966.829011407: ☑️ agreed by iosmanthus.