refactor(tvix/castore): add separate Error enum for archives

The `Error` enum for the `imports` crate has both filesystem and archive
specific errors and was starting to get messy.

This adds a separate `Error` enum for archive-specific errors and then
keeps a single `Archive` variant in the top-level import `Error` for all
archive errors.

Change-Id: I4cd0746c864e5ec50b1aa68c0630ef9cd05176c7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11498
Tested-by: BuildkiteCI
Autosubmit: Connor Brewster <cbrewster@hey.com>
Reviewed-by: flokli <flokli@flokli.de>

tvix/glue/src/builtins/errors.rs

@@ -54,6 +54,9 @@ pub enum FetcherError {
     #[error(transparent)]
     Import(#[from] tvix_castore::import::Error),
 
+    #[error(transparent)]
+    ImportArchive(#[from] tvix_castore::import::archive::Error),
+
     #[error("Error calculating store path for fetcher output: {0}")]
     StorePath(#[from] BuildStorePathError),
 }