Release v0.4.0

[8beeeaaat]

Summary

Prepare the v0.4.0 release: add the CHANGELOG entry covering all changes since v0.3.1, rebased on the latest origin/main.

Changes since v0.3.1

• PR fix: treat Z/-00:00 as unknown local offset per RFC 9557 (#22) #23 — treat Z/-00:00 as unknown local offset per RFC 9557 Section 2.2 (Misinterpretation of Z in RFC9557 #22)
• PR fix: accept critical "!" flag on time-zone annotations per RFC 9557 #24 — accept the critical ! flag on time-zone annotations, reject duplicate time-zone annotations, accept offset-derived zones in consistency/strict checks, stop skipping the Etc/GMT consistency check, and reject CriticalLocation without an attachable zone
• PR fix: resolve RFC 9557 compliance findings from expert review #26 — resolve RFC 9557 compliance findings from the pre-release expert review:
  • Format emits offset annotations as [+09:00] (RFC grammar) instead of [+0900], making Parse -> Format -> Parse round trips lossless
  • Duplicate suffix keys are rejected with ErrCriticalExtension when either occurrence is critical (Section 3.3)
  • Strict mode rejects unknown critical suffix keys other than u-ca
  • A second time-zone annotation is rejected even after an ignored unknown zone; a time-zone annotation after a suffix tag violates the grammar ordering and returns ErrInvalidSuffix
  • Format/FormatNano apply CriticalLocation to the timestamp's own zone when Location is unset
  • ParseError implements Unwrap, so sentinel errors match with errors.Is
• PR refactor IXDTF implementation by concern #27 / main-3 — refactor the IXDTF implementation from a monolithic file into focused modules for parsing, formatting, suffix handling, timezone resolution, validation, calendar tags, extensions, and errors, with expanded targeted tests
• Dependabot CI bumps: actions/checkout v7, actions/cache v6, codecov-action v7

Version rationale

Minor bump (0.3.1 -> 0.4.0): the fixes change accept/reject behavior for several inputs, and the public API gains IXDTFExtensions.CriticalLocation and ParseError.Unwrap. The PR #27 refactor preserves the public API while reorganizing implementation internals.

Release steps after merge

git checkout main && git pull
git tag v0.4.0
git push origin v0.4.0

The Release workflow then runs tests and publishes the GitHub Release automatically.

Verification

• go test ./... passes on the rebased release/v0.4.0 branch

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.56%. Comparing base (617dfda) to head (73a7e43).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #25   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files           8        8           
  Lines         329      329           
=======================================
  Hits          321      321           
  Misses          4        4           
  Partials        4        4           

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