Bump version to 11.4.0

[SeriousBug]

Releases the changes accumulated since 11.3.0. Minor bump: one additive feature (allow_missing), rest are internal improvements and a dependency update.

Changes since 11.3.0

• Add allow_missing derive attribute (Add allow_missing derive attribute #22) — new public feature
• Convert macro panics to compile errors (Convert macro panics to compile errors #21)
• Use sorted const table + binary search for embedded get() (Use sorted const table + binary search for embedded get() #24) — perf
• Update sha2 dependency to 0.11 (Update sha2 dependency to 0.11 #25)

Version bumped in all three crates, plus README install snippets. After merge, trigger the release workflow (workflow_dispatch) to publish to crates.io.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.97%. Comparing base (94e4a29) to head (0c80b04).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #26      +/-   ##
==========================================
- Coverage   79.46%   75.97%   -3.50%     
==========================================
  Files           9        9              
  Lines         448      566     +118     
==========================================
+ Hits          356      430      +74     
- Misses         92      136      +44     

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