refactor(tvix/castore/import): restructure error types

Have ingest_entries return an Error type with only three kinds:

 - Error while uploading a specific Directory
 - Error while finalizing the directory upload
 - Error from the producer

Move all ingestion method-specific errors to the individual
implementations.

Change-Id: I2a015cb7ebc96d084cbe2b809f40d1b53a15daf3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11557
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/glue/src/builtins/errors.rs

@@ -6,6 +6,7 @@ use nix_compat::{
 use reqwest::Url;
 use std::rc::Rc;
 use thiserror::Error;
+use tvix_castore::import;
 
 /// Errors related to derivation construction
 #[derive(Debug, Error)]
@@ -52,10 +53,7 @@ pub enum FetcherError {
     Io(#[from] std::io::Error),
 
     #[error(transparent)]
-    Import(#[from] tvix_castore::import::Error),
-
-    #[error(transparent)]
-    ImportArchive(#[from] tvix_castore::import::archive::Error),
+    Import(#[from] tvix_castore::import::IngestionError<import::archive::Error>),
 
     #[error("Error calculating store path for fetcher output: {0}")]
     StorePath(#[from] BuildStorePathError),