Release v3.6.4: bump version, update README (EN/CN), ensure all examples build

- Bump version to 3.6.4 in Cargo.toml
- Update version references in README.md and README_CN.md
- Add RELEASE_v3.6.4.md with English release notes
- All workspace examples verified to compile (cargo build --workspace)
- Remove RELEASE_v3.6.3.md and docs/ASYNC_EXECUTOR_REVIEW.md
- Minor updates in types, lib, transaction_builder, async_executor, executor, params

Made-with: Cursor

src/trading/common/transaction_builder.rs

@@ -25,8 +25,8 @@ fn sol_f64_to_lamports(sol: f64) -> u64 {
     (lamports.min(u64::MAX as f64)).round() as u64
 }
 
-/// Build standard RPC transaction.
-/// Takes Arc/context by reference to avoid clone in worker hot path (Arc::clone is cheap but ref is zero-cost).
+/// Build standard RPC transaction (worker hot path).
+/// Takes Arc/refs only; one Vec allocation (with_capacity), extend_from_slice for business_instructions, no extra clone of payer/rpc/middleware.
 pub async fn build_transaction(
     payer: &Arc<Keypair>,
     _rpc: Option<&Arc<SolanaRpcClient>>,