test: scan write-set merge is byte-order sorted and byte-range filtered (#331)

[s2x]

Description

The transaction scan() merge (TxnReader::finalizeScanResults()) sorted the merged key list with plain sort() (SORT_REGULAR), which compares numeric strings numerically ("9" before "10"), while TiKV orders keys bytewise ("10" before "9"). The in-range filter for write-set keys used the same loose >= / < operators. Since scan() is contractually ordered and callers paginate on the last returned key, the numeric-order merge silently skipped in-between keys. Fixed to byte order (sort(..., SORT_STRING) + strcmp()) and pinned with the tests demanded by the issue.

Closes #331

Changes

• TxnReader::finalizeScanResults(): sort($allKeys, SORT_STRING) (byte order, issue [TEST-11] Add tests for scan result ordering when the write set is merged (byte order vs PHP sort) #331) and write-set in-range filter switched from loose >= / < to strcmp() (byte order)
• TransactionTest: 4 new tests — merged scan with numeric-string keys returns byte order (['10', '9', 'b']) and string-typed keys (fails on pre-fix master); write-set key '9' inside byte range ['10', 'b') is kept after '10' (loose comparison dropped it); write-set key '19' numerically inside ['2', '3') but bytewise outside is filtered out; binary write-set keys "\x00a" / "\xffz" sort and range-filter correctly
• makeScanResponse() test helper now accepts array<string|int, string> (PHP coerces numeric-string literal keys to int) and casts keys back to strings

Changelog

• [TEST-11] under [Unreleased] → Fixed: TxnReader::finalizeScanResults() now merges the transaction write set into scan results in byte order (SORT_STRING sort + strcmp() range filter); numeric-string keys no longer sort numerically. ([TEST-11] Add tests for scan result ordering when the write set is merged (byte order vs PHP sort) #331)

Code Review

• Pending subagent code review