Add inspection methods to Command for testing

[ryanoneill]

Summary

• Add public inspection methods to Command<M>: is_quit(), is_message(), is_batch(), is_async(), is_overlay_push(), is_overlay_pop(), and action_count()
• These methods allow users to test their update() functions by inspecting what kind of command was returned, without needing access to the internal CommandAction enum
• Each method includes doc tests with realistic usage examples and comprehensive unit tests

Test plan

• Added 7 doc tests covering all new methods
• Added 28 unit tests covering positive cases, negative cases, and combined commands
• All existing tests continue to pass
• cargo clippy --all-features -- -D warnings passes with no warnings
• Both files remain under 1000 lines (mod.rs: 799, tests.rs: 832)

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.09%. Comparing base (fa6edbb) to head (5b81257).
⚠️ Report is 32 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #224   +/-   ##
=======================================
  Coverage   92.09%   92.09%           
=======================================
  Files         146      146           
  Lines       12798    12824   +26     
=======================================
+ Hits        11786    11810   +24     
- Misses       1012     1014    +2     

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