Sewerrat

- Added `within=` to `list_registered_directories()` to search for directories within a specified path.
This is more correct than `prefix=` and should be used in the vast majority of cases.

- Added `exists=` to `list_registered_directories()` to filter to (non-)existent directories.

- Support `number=float("inf")` to get all results in `query()`.

- Support non-blocking calls to the SewerRat API in `register()` and `deregister()`.

- Support more filters in `list_registered_directories()`.
- Improved synchronization of cache with the remote in `retrieve_file()`, `retrieve_directory()`.
- Emit diagnostics when the number of query results is truncated in `query()`.
- Added option for non-recursive listing of directory contents in `list_files()`.

- Added `list_registered_directories()` to list the registered directories.