feat: allow underscores in integer literals #612

Job	Run time
build-acvm-js	3m 4s
build-nargo	2m 9s
build-noir-wasm	5m 10s
build-noirc-abi	3m 26s
source-resolver	35s
ACVM JS (Browser)	59s
ACVM JS (Node.js)	17s
noirc_abi	24s
Noir JS	1m 19s
noir-js-backend-barretenberg	26s
noir_codegen	45s
Integration Tests	8m 21s
noir_wasm	46s
End	1s
	27m 42s

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