[bfrancojr]

Fixes #169.

A @dataset row whose last cell is a timestamp, with no space before the ), was refused: (2024-01-02T03:04:05Z) gave 2:2: invalid timestamp: 2024-01-02T03:04:05Z). Lexer::LexTimestamp ran the timestamp to a space, newline, tab, CR, ,, ], }, # or a comment opener, and read the ) into it. protowire-go's endsRun also stops at ). The fix adds ) to cpp's set, so the two lists now match byte for byte.

Evidence

• protowire-go 903b4a7 Parse accepts (2024-01-02T03:04:05Z). cpp main refused it, and accepted (2024-01-02T03:04:05Z, 1) and ts = [2024-01-02T03:04:05Z]. Both measured.
• New test DatasetTimestampCell.EndsAtTheRowsParen parses the row through Parse and through DatasetReader, and checks that the cell is a timestamp with the right text. It fails with src/ stashed and passes with the fix.
• ctest 730/730 locally (macOS). clang-format 18 clean.
• CI on 2cd0e40 (head, rebased onto main 531c586): all 11 checks pass, including ASan + UBSan, the differential against protowire-go, clang-tidy, CodeQL and Windows.

Found while porting Go's mayEndToken for #168, which uses endsRun. Independent of #167.