[electrum] fix Transaction.from_io in fusion.util

Summary:
This fixes a bug that breaks CashFusion when a round of fusion is starting.
Transaction.from_io now requires a list of TxInputs rather than a list of coin dictionnaries.

Test Plan:
python test_runner.py

search for usages of Transaction.from_io, confirm that inputs are all TxInput instances.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14795