pending validation function

[kastolars]

See: #268

context: validation

Make a validation function that does the following:

Given a contract, a pending balance, and a pending state nonce:

• reject if the contract's value is zero
• reject if the sender public key is nil or if hashing it matches the recipient
• reject if the signature is invalid
• reject if the pending balance is less than the contract value
• reject if the contract state nonce is not 1 greater than the pending state nonce
• if rejected, return an error
• if valid, return nil for the error, and the new pending balance and state nonce (3 values)
• the new pending balance is pending balance - contract value
• the new pending state nonce is pending state nonce + 1

[HarryL5004]

Completed