feat: parse ISO 8601 durations

[bernot-dev]

Change type

🆕 New feature or enhancement

Short description

Support parsing ISO 8601 duration strings in ParseDuration.

Fixes

• fixes ISO 8601 Durations #278

Full description

This change adds native support for parsing ISO 8601 durations within the ParseDuration function. It implements a dedicated, zero-allocation parser (ParseISO8601Duration in iso8601_duration.go) that handles all standard ISO 8601 duration designators (years, months, weeks, days, hours, minutes, and seconds), along with positive/negative signs and decimal fraction separators (supporting both dots and commas). By integrating this check into the main ParseDuration entry point, any incoming strings that begin with the P prefix (after trimming spaces and signs) are routed through the ISO 8601 parser. Comprehensive test suites have been introduced in iso8601_duration_test.go and duration_test.go to cover edge cases, validation rules, overflow boundaries, and format correctness.

Checklist

• I have signed all my commits with my name and email (see DCO. This does not require a PGP-signed commit
• I have rebased and squashed my work, so only one commit remains
• I have added tests to cover my changes.
• I have properly enriched go doc comments in code.
• I have properly documented any breaking change.

[codecov]

Codecov Report

❌ Patch coverage is 97.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.02%. Comparing base (7dcda43) to head (ac63017).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
iso8601_duration.go	97.39%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #280      +/-   ##
==========================================
+ Coverage   86.51%   87.02%   +0.50%     
==========================================
  Files          18       19       +1     
  Lines        2469     2589     +120     
==========================================
+ Hits         2136     2253     +117     
- Misses        230      232       +2     
- Partials      103      104       +1     

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[fredbi]

Superseded by #284 . See also my comment to #278 . Thanks for the nudge: we needed that, but there is more to it than an extra parser.