refactor(downloader): take &self across the downloader hierarchy

Concurrent package operations call into the same downloader instances
through Rc<RefCell<dyn DownloaderInterface>>; with &mut self methods
every call holds a RefMut across its awaits, which panics with
'already mutably borrowed' the moment two operations overlap. This is
groundwork for fanning out InstallationManager's download/install
loops (same rework HttpDownloader/CurlDownloader already got).

- DownloaderInterface/ChangeReportInterface/ArchiveDownloader/
  VcsDownloader methods now take &self; as_change_report_interface
  returns &dyn instead of &mut dyn.
- Implementors move their genuinely mutable state behind cells:
  FileDownloader.additional_cleanup_paths, the archive downloaders'
  cleanup_executed, ZipDownloader.zip_archive_object,
  VcsDownloaderBase.has_cleaned_changes, GitDownloader's stash/discard/
  cache maps and GitUtil, SvnDownloader.cache_credentials,
  PerforceDownloader.perforce. FileDownloader.io gains a RefCell layer
  so get_local_changes can keep PHP's NullIO swap under &self.
- ProcessExecutor::execute_async now returns a future that captures
  everything up front instead of borrowing the executor, and call
  sites build the future before awaiting, so no borrow on the shared
  executor is held while a subprocess runs.
- Filesystem::remove_directory_async becomes remove_directory_async_via
  taking the Rc handle: the Filesystem is only borrowed for the sync
  head/tail, never across the rm subprocess await (sync borrow_mut
  users like rename/ensure_directory_exists would otherwise collide).
- DownloadManager async call sites hold shared borrows only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/crates/shirabe/tests/downloader/fossil_downloader_test.rs b/crates/shirabe/tests/downloader/fossil_downloader_test.rs
index e473b2dd..d3b50a9f 100644
--- a/crates/shirabe/tests/downloader/fossil_downloader_test.rs
+++ b/crates/shirabe/tests/downloader/fossil_downloader_test.rs
@@ -87,7 +87,7 @@ fn test_install_for_package_without_source_reference() {
     let package = get_package(None, None);
 
     let (process, _guard) = get_process_executor_mock(vec![], false, Default::default());
-    let mut downloader = get_downloader_mock(None, None, process, None);
+    let downloader = get_downloader_mock(None, None, process, None);
 
     let path = format!("{}/path", working_dir.path().to_string_lossy());
     let result = run(downloader.install(package, &path));
@@ -121,7 +121,7 @@ fn test_install() {
         Default::default(),
     );
 
-    let mut downloader = get_downloader_mock(None, None, process, None);
+    let downloader = get_downloader_mock(None, None, process, None);
     run(downloader.install(package, &working_dir_str)).unwrap();
 }
 
@@ -134,7 +134,7 @@ fn test_updatefor_package_without_source_reference() {
     let source_package = get_package(None, None);
 
     let (process, _guard) = get_process_executor_mock(vec![], false, Default::default());
-    let mut downloader = get_downloader_mock(None, None, process, None);
+    let downloader = get_downloader_mock(None, None, process, None);
 
     let result = run(async {
         downloader
@@ -182,7 +182,7 @@ fn test_update() {
         Default::default(),
     );
 
-    let mut downloader = get_downloader_mock(None, None, process, None);
+    let downloader = get_downloader_mock(None, None, process, None);
     run(async {
         downloader
             .prepare(
@@ -229,7 +229,7 @@ fn test_remove() {
     });
     let filesystem = std::rc::Rc::new(std::cell::RefCell::new(filesystem));
 
-    let mut downloader = get_downloader_mock(None, None, process, Some(filesystem.clone()));
+    let downloader = get_downloader_mock(None, None, process, Some(filesystem.clone()));
     run(async {
         downloader
             .prepare("uninstall", package.clone(), &working_dir_str, None)