Multiprecision refactoring: inverse mod and big_int improvements, checked big_uint operations #1333

Job	Run time
Check Proof Producer / Get zkLLVM run to use artifacts from	6s
Gcc release full Linux testing / Build and test Linux with gcc	51m 32s
Clang release full Linux testing / Build and test Linux with clang	27m 12s
Check Proof Producer / Prepare targets strings	1s
Verify Circuit Proof / Produce and verify proofs	2m 42s
Check Proof Producer / Build prover, generate proofs for circuits	6m 54s
Verify Circuit Proof / Verify proofs	0s
Check Proof Producer / Verify proof-producer proofs with EVM-placeholder / run-tests	1m 36s
	1h 30m 3s

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