fix: signandsendtxs hook returns results

[gagdiez]

Description

Our current signAndSendTransactions hook returns a vector of FinalExecutionOutcome, but people is generally waiting for the actual result

This PR modifies the hook so it returns the result of the Transaction, and not the execution object itself

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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