Parallel decryptions: parallel precompiles implementation

[toml01]

This PR implements the core precompile logic that handles the parallel FHE function calls.

• Implement the parallel FHE calls:
  • When a decrypt/req/sealOutput precompile starts, first check if we already have the result cached already. If so - return it regardless of if we're in a gas estimation, static call or just regular execution.
  • Otherwise, if gas estimation - return the default value (didn't change).
  • If query/static_call - try to do a synchronous call (we're not changing the state here).
  • Otherwise, the Commit flag is on, which means we're trying to asynchronously evaluate the ct.
• Fix a small type assertion bug in DecryptionResults.
• Note that the caching behavior for sealOutput results is a bit different - it doesn't make sense to cache results per-ciphertext, since the result will change based on the input public key - that's why I also implemented the genSealedKey() function that creates a unique id for every (ciphertext,public key) pair request.

1588750400

[toml01]

@eshelB yep thanks, looks like that was the problem