The asizeof() introduced a very heavy overhead which made swhfs unusable
when relying on many asizeof calls (eg: storing history exploration in
the direntry cache with a history containing >1000 commits).

The heuristic to calculate the size of a FuseEntry is based on
experimental results from repositories with various history sizes (10K,
100k, ...)

Closes T2695.

The readdir() endpoint is now O(N) instead of O(N²) since we do not go
through all entries every time, but only those after the readdir()
offset.

- Change class interface to match async interface (eg: iter -> aiter)
- Sync code is now running with `run_in_executor`
- Use aiosqlite as the async interface for sqlite

To stop the process, run: `fusermount -u MNTDIR`.

FUSE bindings to locally mount and navigate (as a virtual file system)
the Software Heritage archive.

- Basic CLI (usage: swh fuse mount SWHID PATH)
- Handle `cnt` and `dir` artifacts
- User-level commands working: ls, cd, cat
- Metadata and blob are cached using SQLite