Package cache locking

[baszalmstra]

Multiple processes are able to write to the package cache at the same time. At this point, they are completely unaware of each other. This could cause problems when multiple processes try to write to the same cache.

To work around this issue we want to introduce file locking. Conda and Mamba both already have a system in place to facilitate this. We should mimic their behavior for compatibility to ensure that when both Rattler and Conda/Mamba write to the cache there are no issues.

@wolfv about the mamba implementation:

The different operating systems (UNIX and Windows) support methods to lock files (e.g. on unix it's fcntl whatever). We started out with the idea of writing the PID of the locking process into the file but that was pretty brittle. We can just rely on the OS to make sure a file is locked or unlocked.

There are a few crates for this but I don't know how good they are.

Network drives don't support file locking so we would need a different solution there.

[baszalmstra]

In #55 a lockfile struct was introduced. Maybe we can reuse that here?

[baszalmstra]

We have not really seen any issues with this in over a year. Im going to close this.