[TKN-522] optionally simulate for compute units, use correct number of default signatures

[jshiohaha]

Description

• When building a transaction, we now provide the correct number of (default) signatures so that the VersionedTransaction will (de)serialize properly
  • NOTE: All existing functions maintain the same interface as before, we just add a new one to use with the BuildTransactionConfig
• Allow caller to completely skip compute unit simulation by providing an exact value
  • Context: there might be times in which the transaction can fail at build time, but we still want to build the transaction

[wjthieme]

🎈