Add test cases increasing coverage in benchmark, lock, debug, create, and check cmds

[GitGuru2003]

This PR adds tests to improve coverage for several archiver commands:

• benchmark_cmd.py: increased coverage by exercising different --mode and compression combinations.
• lock_cmds_test.py: added tests for lock/unlock workflows.
• debug_cmds_test.py: increased coverage from 92% to 96% by hitting additional debug paths.
• create_cmd_test.py: added two --read-special tests covering:
  • direct FIFO with flags_special
  • symlink-to-special with flags_special_follow
• check_cmd_test.py

These tests turn previously uncovered lines in create_cmd.py and related archiver modules from red to green in the coverage report, improving confidence in handling special files and CLI options.

[ThomasWaldmann]

@GitGuru2003 Thanks for the PR!

In case you used AI to generate code: please read it fully (and think about it) before submitting it.

Also check the development section of our docs for some development env setup commands.

[ThomasWaldmann]

@GitGuru2003 did you see my feedback and that the CI tests fail?