feat: make shared memory directory configurable

[pypingou]

Make the shared memory file location configurable via SCORE_LOG_SHM_DIR environment variable while maintaining backward compatibility (defaults to /tmp/).

This enables containerized deployments where both the datarouter and applications run in separate containers and communicate via shared memory files. By configuring a specific subdirectory (e.g., /tmp/score-logging or /dev/shm/logging), containers can share only that directory via volume mounts without exposing the entire /tmp or /dev/shm filesystem, which may be used for other purposes by other applications.

Changes:

• Add path_utils module for shared directory path resolution
• Update writer_factory.cpp to use configurable path
• Update socketserver.cpp to use configurable path
• Auto-create directory if it doesn't exist (0755 permissions)
• Add unit tests for path utilities (6 tests, all passing)
• Update BUILD files to integrate path_utils library

Environment variable:

• SCORE_LOG_SHM_DIR: Directory for shared memory files (default: "/tmp/")

Example usage for containerized datarouter + application:

Both containers set:

export SCORE_LOG_SHM_DIR=/tmp/score-logging

And mount the same volume at /tmp/score-logging

The environment variable also allows flexible deployment for better performance (e.g., /dev/shm on Linux) while ensuring both application and datarouter sides use identical paths.

Notes for Reviewer

Pre-Review Checklist for the PR Author

• PR title is short, expressive and meaningful
• Commits are properly organized
• Relevant issues are linked in the References section
• Tests are conducted
• Unit tests are added

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Unit tests have been written for new behavior
• Public API is documented
• PR title describes the changes

Post-review Checklist for the PR Author

• All open points are addressed and tracked via issues

References

Closes #

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