test: replace spark doctest skips with verified examples

38 wrappers carried `# doctest: +SKIP` because outputs weren't verified at
authoring time. Run each with concrete inputs, capture actual outputs, and
inline the values so the doctests execute and stay correct.

Covers datetime (20), URL (5), bitmap (3), map (3), and remaining hash,
JSON, math, string, conversion, and format_string cases. Net new doctest
coverage: 65 examples now run that were skipped before; total skipped
across the suite drops from 53 to 12.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer