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, 6 insertions, 6 deletions

diff --git a/crates/shirabe/tests/downloader/zip_downloader_test.rs b/crates/shirabe/tests/downloader/zip_downloader_test.rs
index 878c8054..593f3e76 100644
--- a/crates/shirabe/tests/downloader/zip_downloader_test.rs
+++ b/crates/shirabe/tests/downloader/zip_downloader_test.rs
@@ -155,7 +155,7 @@ fn test_error_messages() {
     let process = std::rc::Rc::new(std::cell::RefCell::new(ProcessExecutor::new(Some(
         io.clone(),
     ))));
-    let mut downloader = ZipDownloader::new(
+    let downloader = ZipDownloader::new(
         io,
         config,
         http_downloader.clone(),
@@ -173,13 +173,13 @@ fn test_error_messages() {
     let result: anyhow::Result<()> = (|| {
         let mut loop_ = Loop::new(http_downloader.clone(), None);
         let promise = Box::pin(async {
-            DownloaderInterface::download(&mut downloader, package.clone(), &path, None, true)
+            DownloaderInterface::download(&downloader, package.clone(), &path, None, true)
                 .await
                 .map(|_| ())
         });
         run(loop_.wait(vec![promise], None))?;
         run(DownloaderInterface::install(
-            &mut downloader,
+            &downloader,
             package.clone(),
             &path,
             true,
@@ -198,7 +198,7 @@ fn test_zip_archive_only_failed() {
     let _tear_down = TearDown::new(set_up.test_dir.path().to_path_buf());
 
     ZipDownloader::__set_has_zip_archive(Some(true));
-    let mut downloader = make_downloader(&set_up);
+    let downloader = make_downloader(&set_up);
     let zip_archive = ZipArchive::__mock(ZipArchiveMock {
         open: Ok(()),
         count: 0,
@@ -224,7 +224,7 @@ fn test_zip_archive_extract_only_failed() {
     let _tear_down = TearDown::new(set_up.test_dir.path().to_path_buf());
 
     ZipDownloader::__set_has_zip_archive(Some(true));
-    let mut downloader = make_downloader(&set_up);
+    let downloader = make_downloader(&set_up);
     let zip_archive = ZipArchive::__mock(ZipArchiveMock {
         open: Ok(()),
         count: 0,
@@ -252,7 +252,7 @@ fn test_zip_archive_only_good() {
     let _tear_down = TearDown::new(set_up.test_dir.path().to_path_buf());
 
     ZipDownloader::__set_has_zip_archive(Some(true));
-    let mut downloader = make_downloader(&set_up);
+    let downloader = make_downloader(&set_up);
     let zip_archive = ZipArchive::__mock(ZipArchiveMock {
         open: Ok(()),
         count: 0,