Prepare manta-crypto for Export to OpenZL

[bhgomes]

After discussions with @stechu, we want to try and transition the manta-crypto tools to its own governing organization as a standalone public-good product (of the likes of arkworks and zk-garage). Before we do this, we should prepare the current code for export by finishing a few tasks:

• Move Poseidon into manta-crypto  #225
• Expose groth16 interface in manta-crypto (migrate from manta-pay) #227
• Move arkworks ECC to manta-crypto #228
• Move the R1CS and relevant constructions into manta-crypto  #226
• Lifting embedded scalars to outer scalars #200
• Remove dead code from manta-crypto that we don't want to keep #256
• Use Pre-computed Powers in Scalar Multiplication #24
• Use Fastest Poseidon Implementation #22
• Support scalar mul of arkworks curve using precomputed table #34
• Add Arkworks Backend to manta-crypto #180