Add storage bounds for pallet `staking` #7178

Job	Run time
preflight / preflight	21s
preflight / ci-versions	1s
cargo-check-all-crate-macos	1s
cargo-check-benches	1s
cargo-check-each-crate	1s
test-frame-ui	1s
test-full-crypto-feature	1s
test-node-metrics	1s
node-bench-regression-guard	1s
check-tracing	1s
test-frame-examples-compile-to-wasm	1s
check-metadata-hash	1s
test-deterministic-wasm	1s
All test misc tests passed	1s
	34s

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