[electrum] support newer protobuf library versions

Summary:
The protobuf API changed in recent version of the library. This causes fusion failures when the fusion round is about to start.
Support both the old and new API.

At the moment the protobuf version in the releases (3.20.3) works. To notice the issue you need to run from sources on a recent linux version with a newer protobuf (e.g. Ubuntu 24.04 has 5.28.2 which fails).

This fix is loosely based on https://github.com/Electron-Cash/Electron-Cash/commit/4e59c7e18dbd21aa210473ac48c7aba5e0fe1162

Test Plan: Active Cash Fusion and wait for a succesfull fusion on Ubuntu 24.04

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17670