Replaces 'flock' with mkdir locking

[Johnosezele]

This PR replaces the Linux-specific flock command with a portable directory-based locking in the test.sh script. The change ensures compatibility across different Unix-like systems, including macOS, while maintaining the same functionality.

Testing
The locking mechanism has been verified with the following test cases:

1. Running a single instance of the test script
2. Attempting to run multiple instances concurrently
3. Testing cleanup on normal script completion
4. Testing cleanup on interruption (SIGINT, SIGTERM)

Closes #878

[nothingmuch]

tACK

[coveralls]

Pull Request Test Coverage Report for Build 16359709624

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 85.766%

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Totals
Change from base Build 16354703046:	0.0%
Covered Lines:	7652
Relevant Lines:	8922

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💛 - Coveralls