refactor!: unify call handlers to `CallHandler`

[hal3e]

One CallHandler to rule them all.

What was done:

• I used the type-state pattern on the CallHandler where the states(calls) are ContractCall, ScriptCall and Vec<ContractCall for the multi-call case.

• SubmitResponse got much simpler as we only have one CallHandler now.

• Refactored the fuels-programs crate and added folders to split the code up.

As allays naming ideas are welcome. For example, CallHandler's call should be renamed to something else as it could be one call or multiple calls. call_or_calls sounded weird. Also the Parsable trait could be renamed.

BREAKING CHANGE:

• FuelCallResponse renamed to CallResponse
• ContractCallHandler removed in favor of CallHandler
• ScriptCallHandler removed in favor of CallHandler
• method_hash removed in favor of CallHandler::new_contract_call

Checklist

• [x] I have updated the documentation.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [x] I have added necessary labels.
• [x] I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• [x] I have requested a review from the relevant team or maintainers.