support docs on 'define_named_enum'

[fdefelici]

Description

This patch allows define_name_enum!(..) macro to accept docs comment.
This is needed in case one wants to use this macro in some packages (like stacks-signer) is defined #![forbid(missing_docs)] attribute, otherwise a compilation error is emitted (see issue #5992 for related analisys)

Applicable issues

• fixes macro define_named_enum! not play nicely with #!forbid(missing_docs) #5992

Additional info (benefits, drawbacks, caveats)

The patch is backwards compatible where define_name_enum is used without docs comment.
Basically the docs comment are managed as optional within the macro generation.

Checklist

• Test coverage for new or modified code paths
• Changelog is updated
• Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo
• New integration test(s) added to bitcoin-tests.yml

[obycode]

LGTM. I've never used this meta functionality before so something new I learned today!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.25%. Comparing base (4273af8) to head (ce9cd5d).
Report is 33 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5993      +/-   ##
===========================================
+ Coverage    84.20%   84.25%   +0.04%     
===========================================
  Files          527      527              
  Lines       384140   384171      +31     
  Branches       323      323              
===========================================
+ Hits        323461   323667     +206     
+ Misses       60671    60496     -175     
  Partials         8        8              

Files with missing lines	Coverage Δ
stacks-common/src/util/macros.rs	87.22% <100.00%> (+1.50%)	⬆️

... and 44 files with indirect coverage changes

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