Hide carapace internal command from completions

[M09Ic]

Background

Carapace injects an internal _carapace command for shell completion plumbing. In an interactive console, that implementation detail should not be offered as a normal user command.

Approach

• Hide _carapace recursively after carapace.Gen has initialized completion state.
• Filter _carapace out while converting carapace values into readline completions.
• Keep the change limited to the completion path.

Tests

• Added a regression test with an explicit _carapace subcommand.
• Verified the command is hidden and not returned as a completion value.
• Ran go test ./...

[codecov]

Codecov Report

❌ Patch coverage is 47.05882% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 24.06%. Comparing base (7002774) to head (f84bdda).

Files with missing lines	Patch %	Lines
completer.go	47.05%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
+ Coverage   22.54%   24.06%   +1.52%     
==========================================
  Files          27       27              
  Lines        2045     2057      +12     
==========================================
+ Hits          461      495      +34     
+ Misses       1554     1527      -27     
- Partials       30       35       +5     

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[maxlandon]

Superseded by #87 (merged to main), which recommits this change signed with your authorship preserved, as part of a batch. Thanks @M09Ic!