feat(tvix/store): add rstest-based PathInfoService tests

This introduces rstest-based tests. We also add fixtures for creating
some BlobService / DirectoryService out of thin air.
To test a PathInfoService, we don't really care too much about its
internal storage - ensuring they work is up to the castore tests.

Change-Id: Ia62af076ef9c9fbfcf8b020a781454ad299d972e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11272
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/castore/src/blobservice/mod.rs

@@ -14,7 +14,7 @@ mod object_store;
 mod sled;
 
 #[cfg(test)]
-mod tests;
+pub mod tests;
 
 pub use self::chunked_reader::ChunkedReader;
 pub use self::combinator::CombinedBlobService;

tvix/castore/src/directoryservice/mod.rs

@@ -9,7 +9,7 @@ mod memory;
 mod simple_putter;
 mod sled;
 #[cfg(test)]
-mod tests;
+pub mod tests;
 mod traverse;
 mod utils;