fix: unsigned integers cannot be negated #456

Job	Run time
build-acvm-js	3m 18s
build-noirc-abi	3m 33s
build-nargo	2m 13s
build-noir-wasm	5m 30s
source-resolver	36s
ACVM JS (Node.js)	22s
ACVM JS (Browser)	58s
Noir JS	1m 12s
noirc_abi	24s
noir-js-backend-barretenberg	29s
noir_codegen	39s
noir_wasm	53s
Integration Tests	8m 20s
End	1s
	28m 28s

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