feat: implement `From<Field>` on `BigNum` #280

Job	Run time
Query supported Noir versions	5s
format	5s
Test on Nargo v1.0.0-beta.1	13s
Test on Nargo v1.0.0-beta.0	27s
Test on Nargo nightly	26s
Noir End	1s
	1m 17s

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