chore: pass `import_directive` by reference #4632

Job	Run time
build-nargo	2m 17s
build-noirc-abi	2m 21s
build-acvm-js	2m 14s
build-noir-wasm	2m 39s
ACVM JS (Browser)	1m 16s
ACVM JS (Node.js)	41s
noir-js-backend-barretenberg	40s
Noir JS	1m 37s
noir_codegen	1m 3s
noirc_abi	56s
Integration Tests (Node)	3m 38s
noir_wasm	1m 4s
Integration Tests (Browser)	5m 8s
End	1s
	25m 35s

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