fix: initialise strings as u8 array #410

Job	Run time
build-nargo	2m 12s
build-nargo	2m 12s
build-noir-wasm	59s
build-noir-wasm	5m 4s
build-acvm-js	57s
build-acvm-js	3m 4s
build-noirc-abi	41s
build-noirc-abi	3m 20s
source-resolver	29s
source-resolver	29s
noirc_abi	0s
noirc_abi	25s
noir-js-backend-barretenberg	0s
noir-js-backend-barretenberg	23s
noir_codegen	0s
noir_codegen	52s
ACVM JS (Node.js)	0s
ACVM JS (Node.js)	16s
Noir JS	0s
Noir JS	1m 14s
ACVM JS (Browser)	0s
ACVM JS (Browser)	1m 6s
noir_wasm	0s
noir_wasm	47s
Integration Tests	0s
Integration Tests	8m 22s
End	0s
End	1s
	32m 53s

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