docs(selenium-devtools-py): measure run identity under pytest-xdist

[vishnuv688]

What & why

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Polish (an improvement to an existing feature)
• Breaking change (existing behavior changes for users)
• Documentation
• Internal (build, CI, dependencies, tooling)

Packages touched

• shared (types and contracts)
• core (framework-agnostic capture/reporting)
• elements (published element/snapshot API — @wdio/elements)
• service (WebdriverIO adapter)
• nightwatch-devtools (Nightwatch adapter)
• selenium-devtools (Selenium adapter)
• backend (server)
• app (UI)
• script (page-injected runtime)
• selenium-devtools-py

Notes for reviewers

Screenshots / recordings

[greptile-apps]

Greptile Summary

This PR documents pytest-xdist run identity and adds coverage for shared identity across controller and worker processes.

• Adds pytest-xdist to the Python package’s test dependencies.
• Adds subprocess and xdist integration coverage for inherited run IDs.
• Updates documentation and run-ID commentary with the measured parallel-run behavior.

Confidence Score: 5/5

The PR appears safe to merge with no blocking failure remaining.

No blocking failure remains.

Important Files Changed

Filename	Overview
packages/selenium-devtools-py/tests/test_xdist_run_identity.py	Adds a temporary-project pytest-xdist harness that records controller and worker run identities.
packages/selenium-devtools-py/tests/test_run_id.py	Adds subprocess coverage confirming that a child process inherits the controller-generated run ID.
packages/selenium-devtools-py/pyproject.toml	Adds pytest-xdist to the test extra so parallel identity coverage runs in CI.
packages/selenium-devtools-py/README.md	Documents shared run identity and expected boundaries for parallel pytest runs.
packages/selenium-devtools-py/src/selenium_devtools/run_id.py	Updates explanatory documentation for the existing run-ID behavior without changing runtime logic.

_{Reviews (2): Last reviewed commit: "test(selenium-devtools-py): run the xdis..." | Re-trigger Greptile}