chore: remove unnecessary casts in `BoundedVec` #5968

Job	Run time
build-nargo	2m 25s
build-noirc-abi	1m 46s
build-noir-wasm	3m 39s
build-acvm-js	1m 32s
ACVM JS (Node.js)	38s
ACVM JS (Browser)	1m 32s
noir-js-backend-barretenberg	42s
noirc_abi	51s
noir_codegen	1m 7s
Noir JS	1m 28s
Integration Tests (Node)	3m 43s
noir_wasm	1m 8s
Integration Tests (Browser)	5m 11s
End	1s
	25m 43s

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