idna v3.19

• Restore the std3_rules option, which had no effect since changes to UTS #46 processing in Unicode 16. Note that uts46_remap() defaults to enabling STD3 rules, so direct callers will see input containing non-LDH ASCII characters rejected again.
• Performance improvements to UTS #46 mapping, particularly for ASCII-only domains.
• Test on free-threaded CPython with the GIL disabled and document thread safety.
• Expose the Unicode version of the generated tables as idna.unicode_version, and show it in idna --version.
• Add code, text, codepoint and position attributes to IDNAError so that the failed rule and the offending character can be identified without parsing the exception message.
• The deprecated transitional argument to encode() and uts46_remap() is now completely ignored, and gives a deprecation warning for the latter.
• Reject A-labels that are not the canonical Punycode encoding of their U-label.
• Fix CONTEXTJ violations raising IDNAError instead of InvalidCodepointContext.
• Consistently raise IDNAError for empty labels and non-ASCII bytes passed to label helper functions and the incremental codec.
• Add property-based tests, extended fuzzing targets, coverage measurement, and CI checks that the data tables match the generator output.
• Various code quality and tooling improvements.

Thanks to stefan6419846, LouieLuNZ, and Salvatore Corvaglia for contributions to this release.