date: avoid double parsing when resolving timezone abbreviations

[CrazyRoka]

Previously, resolve_tz_abbreviation would parse a date string to calculate the timezone offset, format the result back into a string, and return it. The calling function parse_date would then parse this string a second time.

This change modifies resolve_tz_abbreviation to return an Option<Zoned> directly. If the abbreviation logic succeeds, we avoid the second parsing step and the intermediate string allocations, significantly improving performance for inputs containing timezone abbreviations (e.g., "EST").

[codspeed-hq]

CodSpeed Performance Report

Merging #9997 will improve performance by 87.09%

_{Comparing CrazyRoka:date-optimize-abbreviation (fe65d17) with main (c96b96e)}

Summary

⚡ 3 improvements
✅ 136 untouched
⏩ 30 skipped¹

Benchmarks breakdown

	Benchmark	BASE	HEAD	Efficiency
⚡	file_tz_abbreviations[1000]	29.6 ms	15.9 ms	+86.06%
⚡	file_tz_abbreviations[100]	6.4 ms	5 ms	+27.46%
⚡	file_tz_abbreviations[10000]	294.3 ms	157.3 ms	+87.09%

Footnotes

1. 30 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[sylvestre]

impressive perf win