improves parallelism in window-service recv_window (backport #18446) (#20142)

* sends packets in batches from sigverify-stage (#18446)

sigverify-stage is breaking batches to single-item vectors before
sending them down the channel:
https://github.com/solana-labs/solana/blob/d451363dc/core/src/sigverify_stage.rs#L88-L92

Also simplifying window-service code, reducing number of nested branches.

(cherry picked from commit 7d56fa8363)

# Conflicts:
#	core/src/window_service.rs

* removes backport merge conflicts

Co-authored-by: behzad nouri <behzadnouri@gmail.com>

ci/do-audit.sh

@@ -45,8 +45,5 @@ cargo_audit_ignores=(
   # Blocked on jsonrpc removing dependency on unmaintained `websocket`
   # https://github.com/paritytech/jsonrpc/issues/605
   --ignore RUSTSEC-2021-0079
-
-  # `#[zeroize(drop)]` doesn't implement `Drop` for `enum`s
-  --ignore RUSTSEC-2021-0115
 )
 scripts/cargo-for-all-lock-files.sh stable audit "${cargo_audit_ignores[@]}"