chore: `fetch_file` now returns `&str` instead of a `File` #1148

Job	Run time
build-acvm-js	3m 2s
build-nargo	2m 9s
build-noir-wasm	4m 55s
build-noirc-abi	3m 40s
ACVM JS (Browser)	1m 26s
ACVM JS (Node.js)	30s
Noir JS	1m 43s
noirc_abi	48s
noir_codegen	54s
noir-js-backend-barretenberg	42s
Integration Tests	8m 30s
noir_wasm	52s
End	1s
	29m 12s

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