Ratarmount

- Fix StenciledFile accidentally throwing an exception when accessing empty files.
- Improve performance when using union mounting by using a folder-to-archive lookup cache.
- Implicitly added parent folders will now show a size of 0B instead of arbitrary 1B.
- Fix version ordering for implicitly added folders.
- Fix permissions to not remove write permissions. FUSE will still return a
"Read-only file system" error when trying to modify the file system.
- Fix RAR files were not found when ratarmount was daemonized and changed the current working directory.

- Fix recursive mounting failing for archives in top-level directory.
- Replace the optional lzmaffi dependency with a python-xz dependency.
- Fix missing files in ZIP and RAR if parent folders are not in the archive.
- Fix archives getting misrecognized as ZIP because of lenient zipfile.is_zipfile function.
- Make indexed_zstd an optional dependency on macOS because wheels are missing.
- Fix CRC errors thrown by rarfile when reading after seeking back file objects for files inside RARs.
- Fix ratarmount not working if rarfile or zipfile were not installed.
- Disable ZIP support with Python 3.6 and older because the returned file object is not seekable.

- Refactor the code and introduce a MountSource interface.
- Add support for zip and rar archives including password-encrypted ones.
- Improve recursive mounting. If supported by the decompression backend,
compressed archives inside compressed archives can be mounted recursively.
- Fixes for macOS and Windows.

- Fix "BLOB longer than INT_MAX bytes" error for .gz archives larger than ~400GB.
- Add missing "dataclasses" dependency for Python 3.6.
- Open SQLite index read-only to allow multiple ratarmount instances to use it.
- Raise exception if SQLiteIndexedTar cannot read given file object.
- Warn on newer index versions.
- Add support for "--index-name :memory:" to create in-memory indexes.

- Fix SQLiteIndexedTar class when being called with a file object.
- Add -P argument option to activate the parallel BZ2 decoder of indexed_bzip2 1.2.0.
- Add --lazy option, which works in tandem with --recursive, and bind mounted folders.
TARs inside the source folder will be mounted only after the first access to it through the mount point.
- TARs containing hard links to files with exactly the same name will be interpreted as referring
to a prior version of that file.

- Add CLI options --index-file and --index-folder to specify an index location or folder.
- Add support for zstd compressed TARs.
- Add support for xz compressed TARs when compressed with pixz or pxz or similar tools
limiting the block size.
- Fix index location check not accounting for SQLite special requirements.
- Add warnings for when the existing index was created with different arguments,
e.g., without --recursive, even though --recursive was requested.
- Add specialized exceptions used by ratarmount.
- Add recursive mounting for folders in order to mount all contained TARs.