Initial commit: snapshot of spesmilo/electrumx 2.0.0

Unmodified source tree of upstream commit 280cb339aa158e099eb936033eecd15719770651
("Merge pull request #389 from SomberNight/202607_release_2_0",
https://github.com/spesmilo/electrumx, release 2.0.0, 3 July 2026).

All Palladium-specific changes are in the commits that follow.

docs/protocol.rst

@@ -0,0 +1,7 @@
+Electrum Protocol
+=================
+
+See rendered `protocol docs here <https://electrum-protocol.readthedocs.io/>`_,
+
+and `git repository here <https://github.com/spesmilo/electrum-protocol>`_.
+