gh-135253: Document tarfile stream restrictions and examples - #159836

Document the forward-only behavior of tarfile stream modes at the lookup, listing, and extraction methods. Explain when to pass the current TarInfo object and why listing or looking up members can prevent later extraction.

Add a streaming file-reading example, adapt the filtered extractall() example to stream mode, and document StreamError for backward seeking and extracting links as file objects.

Fixes #135253.

Validation:

• Executed the new reading example against a generated gzip archive and checked lookup/list restrictions, link errors, and filtered stream extraction on the current CPython debug build.
• Full HTML documentation build with warnings treated as errors.
• Sphinx lint and patchcheck.

• Issue: tarfile stream restrictions should be documented #135253