Update bigint2 impl with 4096 bit support

[austinabell]

Draft PR until this is released into 1.2 -- as this is pointing to the git version

[austinabell]

Running tests in zkvm using current main (533aff23f633c6102c961d47b9370ec96770de6d), most pass but one hits memory cap (might just be too many tests run and using bump alloc, but will check the specific failure to make sure not an edge case)

running 8 tests
test decode_rsa2048_priv_der ... ok
test decode_rsa2048_priv_pem ... ok
test decode_rsa2048_pub_der ... ok
test decode_rsa2048_pub_pem ... ok
test encode_rsa2048_priv_der ... ok
test encode_rsa2048_priv_pem ... ok
test encode_rsa2048_pub_der ... ok
test encode_rsa2048_pub_pem ... ok

test result: ok. 8 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Running test in guest: /Users/austinabell/development/risc0/RustCrypto-RSA/target/riscv32im-risc0-zkvm-elf/debug/deps/pkcs1v15-d75b7fdbf54859c1 []

running 1 test
test signature_stringify ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Running test in guest: /Users/austinabell/development/risc0/RustCrypto-RSA/target/riscv32im-risc0-zkvm-elf/debug/deps/pkcs1-37c12db8e7c347cb []

running 16 tests
test decode_rsa2048_priv_der ... ok
test decode_rsa2048_priv_pem ... ok
test decode_rsa2048_pub_der ... ok
test decode_rsa2048_pub_pem ... ok
test decode_rsa4096_priv_der ... ok
test decode_rsa4096_priv_pem ... ok
test decode_rsa4096_pub_der ... ok
test decode_rsa4096_pub_pem ... ok
test encode_rsa2048_priv_der ... ok
test encode_rsa2048_priv_pem ... ok
test encode_rsa2048_pub_der ... ok
test encode_rsa2048_pub_pem ... ok
test encode_rsa4096_priv_der ... ok
test encode_rsa4096_priv_pem ... ok
test encode_rsa4096_pub_der ... ok
test encode_rsa4096_pub_pem ... ok

test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Running test in guest: /Users/austinabell/development/risc0/RustCrypto-RSA/target/riscv32im-risc0-zkvm-elf/debug/deps/rsa-ad39eb3288bfe13d []

running 55 tests
test algorithms::generate::tests::key_generation_1024 ... ok
test algorithms::generate::tests::key_generation_128 ... ok
test algorithms::generate::tests::key_generation_multi_16_1024 ... ok
test algorithms::generate::tests::key_generation_multi_3_256 ... ok
test algorithms::generate::tests::key_generation_multi_4_64 ... ok
test algorithms::generate::tests::key_generation_multi_5_64 ... ok
test algorithms::generate::tests::key_generation_multi_8_576 ... ok
test algorithms::generate::tests::test_impossible_keys ... ok
test algorithms::pad::tests::test_left_pad ... ok
test algorithms::pkcs1v15::tests::test_non_zero_bytes ... ok
test algorithms::rsa::tests::recover_primes_works ... ok
test key::tests::build_key_from_p_q ... ok
test key::tests::build_key_from_primes ... ok
test key::tests::invalid_coeff_private_key_regression ... ok
test key::tests::key_generation_1024 ... ok
test key::tests::key_generation_128 ... ok
test key::tests::key_generation_multi_16_1024 ... ok
test key::tests::key_generation_multi_3_256 ... ok
test key::tests::key_generation_multi_4_64 ... ok
test key::tests::key_generation_multi_5_64 ... ok
test key::tests::key_generation_multi_8_576 ... ok
test key::tests::reject_oversized_private_key ... ok
test key::tests::test_from_into ... ok
test key::tests::test_negative_decryption_value ... ok
test oaep::tests::test_decrypt_oaep_invalid_hash ... ok
test oaep::tests::test_decrypt_oaep_invalid_hash_traits ... ok
test oaep::tests::test_encrypt_decrypt_oaep ... ok
test oaep::tests::test_encrypt_decrypt_oaep_traits ... ok
test pkcs1v15::tests::test_decrypt_pkcs1v15 ... ok
test pkcs1v15::tests::test_decrypt_pkcs1v15_traits ... ok
test pkcs1v15::tests::test_encrypt_decrypt_pkcs1v15 ... ok
test pkcs1v15::tests::test_encrypt_decrypt_pkcs1v15_traits ... ok
test pkcs1v15::tests::test_sign_pkcs1v15 ... ok
test pkcs1v15::tests::test_sign_pkcs1v15_digest_signer ... ok
test pkcs1v15::tests::test_sign_pkcs1v15_signer ... ok
test pkcs1v15::tests::test_sign_pkcs1v15_signer_sha2_256 ... ok
test pkcs1v15::tests::test_sign_pkcs1v15_signer_sha3_256 ... ok
test pkcs1v15::tests::test_unpadded_signature ... ok
test pkcs1v15::tests::test_unpadded_signature_hazmat ... ok
test pkcs1v15::tests::test_verify_pkcs1v15 ... ok
test pkcs1v15::tests::test_verify_pkcs1v15_digest_signer ... ok
test pkcs1v15::tests::test_verify_pkcs1v15_signer ... ok
Error: Guest panicked: Out of memory!
test pss::test::test_sign_and_verify_2049bit_key ...

[austinabell]

Update on the above, running tests without that test passes all, and running just that test in isolation works fine. It's just a very large execution with a profile that looks like this:

(not sure if a use case we want to focus on adding a precompile for)