Improves the robustness of integration test scripts

[sashacmc]

Description

This PR improves the robustness of integration test scripts for local development environments.

What does this PR do?

tests/routed.sh:

• Fixes TESTDIR to use absolute path instead of relative path (prevents cp failures)
• Adds cleanup for corrupted zenohd state from interrupted runs
• Validates zenohd binary exists and is executable before use
• Verifies zenohd process started successfully before running tests
• Checks if process is running before attempting to terminate it

CMakeLists.txt:

• Replaces configure_file() with file() for test scripts to explicit execute permissions on copied scripts

Why is this change needed?

The integration test scripts had several issues when running locally

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Labels: internal

🏠 Internal Change

This PR is marked as internal (not user-facing):

• No API changes - Public APIs unchanged
• No behavior changes - External behavior identical
• Refactoring/maintenance - Code improvements only
• Tests still pass - All existing tests pass without modification

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[gmartin82]

Looks good.