Fix kernel URL references for kernel_read and kernel client

[fallintoplace]

Why

The kernel documentation accepts Kaggle code URLs, but the kernel_read CLI and KaggleKernelClient previously expected owner/slug references. A full URL could therefore be parsed as the wrong owner and slug.

What changed

• Normalize Kaggle code URLs to owner/slug at the CLI boundary and in KaggleKernelClient.
• Print a note to stderr when scriptVersionId is present because kernel_read fetches the latest kernel version. Use kernel_archive.py for a specific historical version.
• Add regression coverage for URL references, owner/slug references, and the warning behavior.

Validation

• uv run pytest

[daxiongshu]

Thank you! Nice fix — one small thing before merge. Versioned URLs like
https://www.kaggle.com/code/jiweiliu/kaggle-agent-ensemble-with-yash9439?scriptVersionId=312497119
normalize fine, but the scriptVersionId gets silently dropped and kernel_read fetches the latest version. Do I get this right? If so, can we warn instead of staying silent? Something like:

normalized_kernel_ref = kernel_ref(args.kernel_ref)
if "scriptVersionId=" in args.kernel_ref:
    print(
        "Note: scriptVersionId is ignored — kernel_read always fetches the latest "
        "version. Use kernel_archive.py to fetch a specific historical version."
    )

Everything else LGTM — tests pass locally against latest main. 👍

[fallintoplace]

Thank you for the review, I have pushed the fix.