Introduce new TransactionWithSignature interface

[kirugan]

Right now all transactions implement Signature() method, but we don't need it for L1Handler and Deploy transactions (right now they return empty slice).
We already faced some issues with it, here is an example:

if txSignature := transaction.Signature(); len(txSignature) > 0 {
   digest.Update(txSignature...)
} else {
   digest.Update(&felt.Zero)
}

it was rewritten as:

switch transaction.(type) {
  case *DeployTransaction, *L1HandlerTransaction:
     digest.Update(&felt.Zero)
  default:
    digest.Update(transaction.Signature()...)
}

but code above may lead to more questions: why we're specifying exactly these transactions? is it specific to this function only or applicable to entire codebase?

It can be solved by introducing new interface type TransactionWithSignature (name only for example, I'm pretty sure there is a better naming):

type TransactionWithSignature interface {
   Signature() []*felt.Felt
}

which can be used in example above as:

switch transaction.(type) {
case TransactionWithSignature:
     digest.Update(transaction.Signature()...)
default:
     digest.Update(&felt.Zero)
}

[pri-3x]

@kirugan PR for this issue is opened: #2189
The workflows are awaiting approval to run. Could you please review and approve them?