chore: simplify how blns is loaded into tests #5491

Job	Run time
build-acvm-js	1m 43s
build-nargo	2m 20s
build-noirc-abi	1m 45s
build-noir-wasm	3m 53s
noirc_abi	42s
noir-js-backend-barretenberg	50s
ACVM JS (Browser)	1m 32s
ACVM JS (Node.js)	36s
noir_codegen	1m 7s
Noir JS	1m 27s
Integration Tests (Node)	3m 36s
noir_wasm	1m 4s
Integration Tests (Browser)	5m 5s
End	1s
	25m 41s

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