Parallel multi-SWQoS submit: builder pool and executor tweaks

- transaction_pool: add PARALLEL_SENDER_COUNT (18), ensure prefill >= 18 so
  multi-channel build never serializes; prefill 64 with max(PREFILL, 18)
- async_executor: document that pool prefill must match sender thread count
- executor: do not sort submit_timings (avoids any extra work); comment that
  log order is completion order
- docs: add ASYNC_EXECUTOR_REVIEW.md
- remove RELEASE_NOTES_v3.6.2.md; minor example/types/lib/params updates

Made-with: Cursor

examples/middleware_system/src/main.rs

@@ -31,7 +31,7 @@ impl InstructionMiddleware for CustomMiddleware {
     fn process_protocol_instructions(
         &self,
         protocol_instructions: Vec<Instruction>,
-        _protocol_name: String,
+        _protocol_name: &str,
         _is_buy: bool,
     ) -> Result<Vec<Instruction>> {
         // do anything you want here
@@ -42,7 +42,7 @@ impl InstructionMiddleware for CustomMiddleware {
     fn process_full_instructions(
         &self,
         full_instructions: Vec<Instruction>,
-        _protocol_name: String,
+        _protocol_name: &str,
         _is_buy: bool,
     ) -> Result<Vec<Instruction>> {
         // do anything you want here