Fix warnings and deprecation messages in test suite

[seonghobae]

Description

Running the test suite on main currently yields a warning:
RuntimeWarning: 'bandscope_analysis.cli' found in sys.modules after import of package 'bandscope_analysis', but prior to execution of 'bandscope_analysis.cli'; this may result in unpredictable behaviour

Other deprecation warnings (librosa, audioread) were addressed in separate feature branches (PR #149). This issue tracks fixing the remaining root causes of runtime warnings during pytest execution.

Root Cause Analysis

• The RuntimeWarning is caused by testing runpy.run_module against a module that is already imported at the top of the test file (test_cli.py). Python's runpy issues a warning when doing this because running an already-imported module as __main__ can cause side effects.

Action Plan

• Refactor the test or the import logic in test_cli.py to eliminate the RuntimeWarning.
• Ensure all tests run with 0 warnings on the default branch.

[coderabbitai]

🔗 Related PRs

#99 - chore: fix cargo audit warnings and python test coverage warnings [merged]

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[seonghobae]

Current default-branch verification after PR #185 shows the Python test warning class from this issue is resolved.

Evidence from fresh worktree stepwise/pr185-postmerge at a84d1a1ace3228e947eca0f6d785095d5520b2b0:

• BANDSCOPE_ENABLE_RUST_CHECK=1 ./scripts/harness/quickcheck.sh completed successfully.
• Python analysis engine pytest collected 191 tests and reported 191 passed with 100% coverage.
• No runpy/bandscope_analysis.cli RuntimeWarning appeared.

New non-Python post-merge supply-chain findings are tracked separately in #187 and #188.