First step towards denying clippy::integer_arithmetic (bp #15366) (#15381)

* CI: Globally deny clippy::integer_arithmetic lint

(cherry picked from commit 7035e8485c)

* Re-allow clippy::integer_arithmetic at crate-level

(cherry picked from commit 7f7370c306)

# Conflicts:
#	bench-tps/tests/bench_tps.rs

Co-authored-by: Trent Nelson <trent@solana.com>

ledger/benches/protobuf.rs

@@ -1,3 +1,4 @@
+#![allow(clippy::integer_arithmetic)]
 #![feature(test)]
 extern crate test;
 

ledger/src/lib.rs

@@ -1,4 +1,5 @@
 #![cfg_attr(RUSTC_WITH_SPECIALIZATION, feature(specialization))]
+#![allow(clippy::integer_arithmetic)]
 #[macro_use]
 extern crate solana_bpf_loader_program;
 

ledger/tests/shred.rs

@@ -1,3 +1,4 @@
+#![allow(clippy::integer_arithmetic)]
 use solana_ledger::entry::Entry;
 use solana_ledger::shred::{
     max_entries_per_n_shred, verify_test_data_shred, Shred, Shredder,