use github fast path to check for changes before doing the git pull

[syphar]

Coming from this zulip thread, looking at:

• https://github.com/rust-lang/cargo/blob/edd36eba5e0d6e0cfcb84bd0cc651ba8bf5e7f83/src/cargo/sources/git/utils.rs#L1396
• https://docs.github.com/en/rest/commits/commits?apiVersion=2022-11-28#get-a-commit

it seems to be recommended by github to use the fast path to check if there are changes, before actually doing the git pull.

This is for just just a (working) draft PR that needs some work around errors & tests, but I wanted to check with you if the approach is fine before I invest more work.

With this change I would probably change docs.rs to check the index more often, so we see requests more often.

[syphar]

@Byron what do you think?

[Byron]

That sounds like a very good idea, please go for it!

There should also be some tests that clone from GitHub already on CI, so I'd expect the code to run already. Thus I'd think not much has to be done except for maybe assuring that it doesn't break non-GitHub.

For that, maybe have some unit tests around the 'is this a GitHub URL' to be sure it will work for other URLs as well, that should suffice.

[syphar]

r? @Byron

[syphar]

btw, I removed the feature-flag again, thinking that we should actually never provide the option not to use the fast-path for github.

Of course we might have unnecessary dependencies for non-github indexes, though reqwest is already in the tree from gix-transport

[syphar]

Of course I can add it back and make it optional

[Byron]

Looks very good, thanks a lot for contributing!

[Byron]

And here is a new release, with gix upgrade: https://github.com/Byron/crates-index-diff-rs/releases/tag/v26.0.0