feat(tvix/glue/store_io): have KnownPaths track fetches too

Have fetcher builtins call queue_fetch() whenever they don't need to
fetch something immediately, and teach TvixStoreIO::store_path_to_node
on how to look up (and call ingest_and persist on our Fetcher).

Change-Id: Id4bd9d639fac9e4bee20c0b1c584148740b15c2f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11501
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>

tvix/glue/src/fetchers.rs

@@ -19,7 +19,7 @@ use tvix_store::{pathinfoservice::PathInfoService, proto::PathInfo};
 use crate::{builtins::FetcherError, decompression::DecompressedReader};
 
 /// Representing options for doing a fetch.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum Fetch {
     /// Fetch a literal file from the given URL, with an optional expected
     /// NixHash of it.