Respect --kernel and --language in --help-notebook

[fzlzjerry]

What does this PR do?

--help-notebook returned through the inspection path without forwarding the
CLI's --kernel or --language values, so translator selection relied only on
notebook metadata. This change threads both overrides through that path.

Parameter inference now uses an exact registered kernel translator without
requiring separate language metadata. For unregistered or custom kernels, it
continues to fall back to the supplied or notebook language. CLI regression
coverage exercises both kernel cases and the explicit language override.

Validation:

• pytest papermill/tests -q (550 passed)
• pre-commit run --files papermill/cli.py papermill/inspection.py papermill/tests/test_cli.py
• check-manifest

Fixes #905

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