Multiprecision refactoring: inverse mod and big_int improvements, checked big_uint operations #1363

Job	Run time
Gcc release full Linux testing / Build and test Linux with gcc	41m 42s
Clang release full Linux testing / Build and test Linux with clang	39m 44s
Check Proof Producer / Prepare targets strings	1s
Check Proof Producer / Get zkLLVM run to use artifacts from	8s
Verify Circuit Proof / Produce and verify proofs	3m 3s
Check Proof Producer / Build prover, generate proofs for circuits	7m 9s
Verify Circuit Proof / Verify proofs / verify-proofs	1m 30s
Check Proof Producer / Verify proof-producer proofs with EVM-placeholder / run-tests	1m 37s
	1h 34m 54s

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