migrate pallet-fast-unstake to bench v2 syntax #5189

Job	Run time
preflight / preflight	43s
preflight / ci-versions	1m 18s
cargo-check-benches (master)	21m 15s
cargo-check-benches (current)	23m 2s
test-frame-ui	46m 7s
cargo-check-each-crate (1)	23m 36s
cargo-check-all-crate-macos	10m 39s
cargo-check-each-crate (2)	21m 3s
cargo-check-each-crate (3)	8m 46s
test-full-crypto-feature	2m 43s
test-node-metrics	11m 2s
cargo-check-each-crate (4)	21m 4s
cargo-check-each-crate (5)	29m 2s
cargo-check-each-crate (6)	14m 51s
cargo-check-each-crate (7)	30m 19s
test-frame-examples-compile-to-wasm	3m 24s
test-deterministic-wasm	7m 48s
check-tracing	2m 27s
check-metadata-hash	7m 6s
node-bench-regression-guard	17s
All test misc tests passed	1s
	4h 46m 33s

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