Fix telemetry workflow configuration

[aldro61]

Summary

Fixes the pool telemetry workflow that was added in #121:

• Rename workflow file from monitor-pool-usage.yml to pool-telemetry.yml to avoid confusion with the existing instance pool monitoring workflow
• Fix module import error by installing from dev/requirements.txt which includes the local package (-e ..)
• Update workflow name to "Pool Usage Telemetry"
• Update Python version to 3.12 (matching the other workflows)
• Add pip cache for faster builds

This resolves the ModuleNotFoundError: No module named 'browsergym.workarena' error encountered in the GitHub Actions workflow.

Test plan

• Verify workflow runs successfully in GitHub Actions
• Confirm telemetry data is logged to W&B

Fixes the issues found after merging #121.

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