feat!: improve transaction builders wrt TxPolicies

[hal3e]

This PR improves the usage of TxPolicies and fixes some of the issues that remained after their were introduced.

BREAKING CHANGE:

• ScriptTransactionBuilder and CreateTransactionBuilder do not have with_maturity and with_gas_price, (with_gas_limit). They are set through the with_tx_policies method.
• Maturity is not set to 0 by default - instead we use an Option<u64> and None if it was not set. This saves bytes as it is not serialized if None
• WitnessLimit is set to the size of all witnesses in the builder. If the user uses append_witnesses after finalizing the transaction a new error will be returned that helps the user set the witness limit manually.

Checklist

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

[MujkicA]

I left some questions

[digorithm]

Super clean, great job!