[Refactor] change TransactionRequest to field to Option<TxKind>

[prestwich]

• Modify to field to make creates explicit
• Error on non-4844 build if to is unset
• Error on 4844 build if to is unset or create
• Add following to the builder trait

  • fn as_create(self) -> Self shortcut to set the field to Some(Create)

  • fn deploy_code(self, code: Vec<u8>) -> Self to set data and to fields at once

  • fn with_call<T: SolCall>(self, t: T) -> Self to set data and ensure to is NOT Create (set to to None if it is currently Create)

        not convinced we should default to create instead of erroring if not specifically set to create, as creating with `value` and empty data is a valid tx that burns user funds. We should probably error on building if `to` is unset, and provide a shortcut for `.create()`
    

Originally posted by @prestwich in #505 (comment)

[EmperorOrokuSaki]

I'll give this a try.