Reject unsupported KCL format output

[JordanNoone]

Summary

• reject YAML and table output explicitly for zoo kcl format
• avoid successful commands that silently produce empty stdout
• keep JSON and default formatted-source output unchanged

Tests

• cargo fmt --check
• ZOO_TEST_TOKEN=dummy cargo test format_kcl_rejects_unsupported_output --no-fail-fast

Closes #1751

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.97%. Comparing base (0c27251) to head (20f718b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1825      +/-   ##
==========================================
+ Coverage   65.94%   65.97%   +0.02%     
==========================================
  Files          43       43              
  Lines        8434     8434              
==========================================
+ Hits         5562     5564       +2     
+ Misses       2872     2870       -2     

Flag	Coverage Δ
unittests	65.97% <ø> (+0.02%)	⬆️

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