URL validation/access fixes

[akx]

Description

I was profiling things and noticed a whole lot of time was spent in is_valid_url and was pretty surprised that that function actually does HTTP requests if it can.

This PR:

• makes that function share a requests session if it needs to do both HEAD + GET
• renames that function to probe_url because that's more what it does, with a deprecation trampoline for possible external users
• changes uses where is_valid_url was only used to check whether another function that does a requests request should be called to the new is_http_url_like function.

While working on that I realized there were small bugs in encode_url_to_base64 and download_tmp_copy_of_file where they didn't check for the response status, and would thus happily end up writing e.g. an error page out.

These changes are in the gradio_client library, but these functions are gratuitously used by gradio itself.

🎯 PRs Should Target Issues

This PR does not target an issue right now, sorry; this was just another small papercut sort of problem I could easily fix.

[gradio-pr-bot]

All the demos for this PR have been deployed at https://huggingface.co/spaces/gradio-pr-deploys/pr-4695-all-demos

[abidlabs]

Nice improvements @akx!

Could we just add some tests for this:

While working on that I realized there were small bugs in encode_url_to_base64 and download_tmp_copy_of_file where they didn't check for the response status, and would thus happily end up writing e.g. an error page out.

Should be good to merge then

[abidlabs]

Thank you very much @akx!