Add storage bounds for pallet `staking` #6875

Job	Run time
preflight / preflight	37s
preflight / ci-versions	1m 13s
cargo-check-all-crate-macos	5m 47s
cargo-check-benches (master)	4m 59s
cargo-check-each-crate (1)	4m 35s
cargo-check-benches (current)	4m 54s
test-frame-ui	6m 48s
cargo-check-each-crate (2)	4m 28s
cargo-check-each-crate (3)	4m 33s
cargo-check-each-crate (4)	4m 33s
test-full-crypto-feature	2m 45s
test-node-metrics	5m 59s
cargo-check-each-crate (5)	4m 33s
cargo-check-each-crate (6)	4m 35s
cargo-check-each-crate (7)	4m 36s
test-frame-examples-compile-to-wasm	1m 25s
node-bench-regression-guard	11s
check-tracing	0s
check-metadata-hash	0s
test-deterministic-wasm	1s
All test misc tests passed	1s
	1h 6m 33s

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