docs: update changelog for v0.14.0 release

[kolkov]

Summary

• Add PR feat: enumerate dense link storage on group load #55 entry (dense link storage enumeration, @rhaist)
• Add PR test(dense): add NetCDF-4 dense-link fixture + read test #56 entry (dense link fixture, @rhaist)
• Add PR feat: object deletion support — Delete(), GroupWriter.DeleteAttribute(), allocator Free() (Issue #51) #57 entry (object deletion support, Issue Support Deletion of Attributes/Groups/Datasets #51)
• Set version to v0.14.0 (2026-06-25)

Test plan

• Documentation only — no code changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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