Include the Python runtime in CLI version output

[ac1982]

Include the running Python version in pylsp --version and pylsp -V, for example pylsp v1.15.0 (Python 3.12.15). This helps identify the server runtime when it was installed through pipx or a separate environment.

Reuse the existing argparse version action. The README clarifies that this runtime can differ from a plugin's configured interpreter or lint target. Subprocess tests cover both flags and successful exit without server startup.

Related to #706; this addresses runtime identification, not plugin-version enumeration.

Validation:

• New tests fail before and pass after.
• Full suite in the upstream CI environment: 204 passed, 9 skipped.
• Ruff checks and formatting pass for pylsp and test.
• Installed console command verified on Python 3.9 and 3.12 (Linux ARM64).

AI assistance: implemented and tested with Codex.