`orig_url` was unclear. Whose origin? `remote_url` is way more
self-explanatory under a `git fetch` context.

The explanation is moved to be public from an inline comment.

Although this is only a few lines of code, I think it is still worth
keeping it clean if it's not used by Cargo internally. Not to mention
this apparently has an alternative solution at this moment, for example:

```diff
- let oid = git_remote.rev_for(db_path, git_ref)?;
+ let oid = git_remote.db_at(db_path)?.resolve(git_ref)?;
```

From a naive research on GitHub, there is only one usage[^1] and it
seems to be active but still experimental. Pardon my abrupt change
breaking your project :(

Only when we start considering what we want to expose can Cargo has
a clearer boundaries between its subcrates.

[^1]: https://github.com/trustification/source-distributed/blob/124ef26081a41330a553483441fca544bedbb473/src/git.rs#L34

It doesn't seem that they need to derive `Serialize`. Is there any other
usage I am not aware of?

It was confusing and may lead to inconsistency that people need to
pass both `path` and `repo` and ensure they are in sync.

This should be less controversial as the current logic share the
same `GitRemote`. You can see the callsite of `GitDatabase::copy_to`
use `self.url()`, which then calls into `self.remote.url(). When a
`GitDatabase` is created, Cargo also uses `self.remote` as the
remote of that `GitDatabase`.