Always use streamed remote compaction for supported providers (#44255)

## What changed

- Route manual and automatic remote compaction through the v2 implementation.
- Retire the `remote_compaction_v2` feature toggle while continuing to advertise it in the model client beta features header.
- Migrate compaction tests from `/responses/compact` to streamed `/responses` requests with `compaction_trigger` items and remove legacy parity coverage.

## Testing

Add streamed compaction coverage for tool search output trimming and session base instruction token estimates. Update app-server tests to verify started/completed notifications for both local and streamed remote compaction.

GitOrigin-RevId: cea392a6166a9b116ff83708fd9126d5546476e4

codex-rs/core/tests/suite/mod.rs

@@ -56,7 +56,6 @@ mod codex_delegate;
 mod collaboration_instructions;
 mod compact;
 mod compact_remote;
-mod compact_remote_parity;
 mod compact_resume_fork;
 mod context_annotations;
 mod current_time_reminder;