Add sync_identifier orchestration and ThrottleManager queue processing

Implement the main sync orchestration function and trigger-based queue
processing for throttled domains:

sync_identifier function:
- Orchestrates syncing git data for a single identifier
- Tries all non-throttled URLs in sequence
- Checks completion after each fetch (no pending events or all OIDs fetched)
- Enqueues with throttled domains when non-throttled URLs are exhausted
- Returns true if complete, false if events remain (for backoff)

ThrottleManager enhancements:
- Add set_context() to provide SyncContext for queue processing
- Add try_process_next() to spawn tasks when capacity frees
- Add process_queued_identifier() to handle queued work
- Update complete_request() to trigger processing on completion
- Update enqueue_identifier() to trigger processing when capacity available
- Add internal methods for non-Arc testing compatibility

Generic function updates:
- Add ?Sized bound to sync_identifier_next_url, sync_identifier_from_url,
  sync_identifier, and get_throttled_domains_with_untried_urls for
  dynamic dispatch support (Arc<dyn SyncContext>)

Tests:
- sync_identifier_tries_multiple_urls_until_complete: verifies sequential
  URL fetching until all OIDs are available
- sync_identifier_enqueues_throttled_domains_when_incomplete: verifies
  throttled domains get the identifier enqueued for later processing
- has_queued_work_reflects_queue_state: verifies queue state tracking

1 files changed, 2 insertions, 2 deletions

diff --git a/src/purgatory/sync/mod.rs b/src/purgatory/sync/mod.rs
index d26c1f0..8ac9216 100644
--- a/src/purgatory/sync/mod.rs
+++ b/src/purgatory/sync/mod.rs
@@ -13,8 +13,8 @@ mod throttle;
 
 pub use context::{ProcessResult, SyncContext};
 pub use functions::{
-    get_throttled_domains_with_untried_urls, sync_identifier_from_url, sync_identifier_next_url,
-    ThrottledDomainInfo,
+    get_throttled_domains_with_untried_urls, sync_identifier, sync_identifier_from_url,
+    sync_identifier_next_url, ThrottledDomainInfo,
 };
 pub use queue::SyncQueueEntry;
 pub use throttle::{DomainThrottle, ThrottleManager};