feat: shortcircuit merging two of the same value during flattening #5434

Job	Run time
build-noirc-abi	2m 32s
build-nargo	2m 33s
build-noir-wasm	3m 57s
build-acvm-js	3m 10s
noirc_abi	1m 16s
noir-js-backend-barretenberg	41s
Noir JS	1m 31s
noir_codegen	1m 2s
ACVM JS (Browser)	1m 14s
ACVM JS (Node.js)	39s
noir_wasm	1m 4s
Integration Tests (Node)	3m 53s
Integration Tests (Browser)	5m 10s
End	1s
	28m 43s

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