fix: prevent concurrent access to repodata files with lock

[tl-hbk]

Description

I've been trying to run multiple rattler-build processes concurrently and ran into a few issues mentioned here.

prefix-dev/rattler-build#1149

Whenever rattler_index::index was called it would error either because another process was trying to also call rattler_index::index or a SparseRepoData had one of the files memory mapped. This PR adds locks to both locations.

The name of the lock files used match the one already used by rattler_repodata_gateway::fetch::fetch_repo_data

[tl-hbk]

After testing this with rattler-build for a bit this ocassionally deadlocks if multiple processes want the locks for the same files but acquire them in different order

EDIT: Switched to open_ro on the lock which I think shouldn't block other processes from using the SparseRepoData but should prevent index from getting an exclusive lock. I think I'll need to add another lock before SparseRepoData are created or when fetch_repo_data is called and hold onto that first so that the order of the rest of the locks doesn't cause issues