refactor(tvix/castore): add PathComponent type for checked components

This encodes a verified component on the type level. Internally, it
contains a bytes::Bytes.

The castore Path/PathBuf component() and file_name() methods now
return this type, the old ones returning bytes were renamed to
component_bytes() and component_file_name() respectively.

We can drop the directory_reject_invalid_name test - it's not possible
anymore to pass an invalid name to Directories::add.
Invalid names in the Directory proto are still being tested to be
rejected in the validate_invalid_names tests.

Change-Id: Ide4d16415dfd50b7e2d7e0c36d42a3bbeeb9b6c5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12217
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/store/src/import.rs

@@ -3,6 +3,7 @@ use std::path::Path;
 use tracing::{debug, instrument};
 use tvix_castore::{
     blobservice::BlobService, directoryservice::DirectoryService, import::fs::ingest_path, Node,
+    PathComponent,
 };
 
 use nix_compat::{
@@ -139,14 +140,19 @@ where
         )
     })?;
 
-    let name = bytes::Bytes::from(output_path.to_string());
+    let name: PathComponent = output_path
+        .to_string()
+        .as_str()
+        .try_into()
+        .expect("Tvix bug: StorePath must be PathComponent");
+
     log_node(name.as_ref(), &root_node, path.as_ref());
 
     let path_info = derive_nar_ca_path_info(
         nar_size,
         nar_sha256,
         Some(&CAHash::Nar(NixHash::Sha256(nar_sha256))),
-        output_path.to_string().into_bytes().into(),
+        name.into(),
         root_node,
     );