Cannot fetch unless a remote is defined

Hi,

Thank you for pygit2! I'm using it extensively for git tooling in Ubuntu, but occasionally I find some corner where a feature doesn't exist and I have to resort to calling a git subprocess.

The git CLI allows me to use git fetch without having a remote defined. I can just specify a URL. I can't find any documentation on this in pygit2 though. It looks like I have to define a remote, with a name, first. Since I don't necessarily own the repository, this requires an ugly workaround because I have to be concerned about name collisions, crashing without having removed a temporary remote, etc.

Any chance of adding API functionality to fetch (and presumably) push against remotes with just a URL and no mandatory repository configuration please?

Start by reviewing pygit2's existing remote-definition and fetch/push entry points alongside the git CLI behavior described in the issue. Determine how URL-only fetch and push should work without creating a named remote, then verify the behavior with focused tests; done means both operations accept a URL without requiring repository configuration.