Matching vectors with python implementation

[armfazh]

This is the implementation that uses the CSRNG API discussed in mmaker/draft-irtf-cfrg-sigma-protocols#123

This implementation passes the test vectors

• generated with python (Adding CSRNG API to poc code mmaker/draft-irtf-cfrg-sigma-protocols#125)
• Also, it can produce its own test vectors (those with rust_ prefix).

Changes;

• Added Cargo.lock to use the freeze dependencies.
• TODO: spongefish had issues onendianees of scalars
  -- See Encoding of ark_secp256r1 Scalars must be big-endian arkworks-rs/spongefish#78
  -- See p256 scalars must be big-endian (I2OSP and OS2IP) arkworks-rs/spongefish#79)
• G::Scalar needs to implement Codec to properly handle endianess
• Derive challenge function was incorrectly reducing mod p, now it's fixed.
• we can create and check test vectors from both rust and python.

[cathieyun]

Some nits on test vector seeding and documentation, but overall this looks good! (Approving, pending those changes)

[cathieyun]

LGTM!

[cathieyun]

@mmaker can you take a look at this PR?
(Tagging you because I can't explicitly add you as a reviewer, as I don't have admin access.)