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>

sdk/src/lib.rs

@@ -1,5 +1,6 @@
 #![cfg_attr(RUSTC_WITH_SPECIALIZATION, feature(specialization))]
 #![cfg_attr(RUSTC_NEEDS_PROC_MACRO_HYGIENE, feature(proc_macro_hygiene))]
+#![allow(clippy::integer_arithmetic)]
 
 // Allows macro expansion of `use ::solana_sdk::*` to work within this crate
 extern crate self as solana_sdk;