refactor: simplify Spec::merge with local macros

[jdx]

Summary

Replace 14+ repetitive if-check patterns in Spec::merge with three local macros:

• merge_str! for String fields (replace if non-empty)
• merge_opt! for Option fields (replace if Some)
• merge_extend! for Vec/IndexMap fields (extend if non-empty)

This reduces boilerplate and makes the merging strategy for each field immediately clear.

Before: 47 lines with repetitive if patterns
After: 42 lines with declarative macro calls

Test plan

• All tests pass
• No behavior changes - macro expansion produces identical code

🤖 Generated with Claude Code

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Note

Refactors Spec::merge to reduce duplication and clarify merge behavior without changing functionality.

• Introduces local macros: merge_str! (non-empty String), merge_opt! (Option is Some), and merge_extend! (extend non-empty collections)
• Applies macros across name, bin, usage, about*, version, author, disable_help, min_usage_version, default_subcommand, complete, and examples
• Retains existing merges for config (delegated merge) and cmd (self.cmd.merge(...))

^{Written by Cursor Bugbot for commit 5145714. This will update automatically on new commits. Configure here.}

[Copilot]

Pull request overview

This PR refactors the Spec::merge method by replacing repetitive conditional merging patterns with three declarative local macros (merge_str!, merge_opt!, merge_extend!), making the merge strategy for each field type immediately clear while reducing boilerplate code.

Changes:

• Introduced three local macros to handle different field merging strategies (String, Option, and collection types)
• Replaced 14+ repetitive if-check patterns with macro invocations
• Reduced method from 47 to 42 lines while maintaining identical behavior

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.29%. Comparing base (9df7c86) to head (5145714).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/spec/mod.rs	0.00%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #451      +/-   ##
==========================================
- Coverage   47.36%   47.29%   -0.07%     
==========================================
  Files          47       47              
  Lines        6653     6656       +3     
  Branches     6653     6656       +3     
==========================================
- Hits         3151     3148       -3     
- Misses       1739     1742       +3     
- Partials     1763     1766       +3     

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