[electrum] start adding typehints and documentation to network.py

Summary:
Also rename the type alias Request to interfaceRequest in interface.py, so we can add a NetworkRequest type alias in network.py. The two are similar but different.

Depends on D14952

Test Plan:

python test_runner.py
pytest electrumabc/tests/regtest

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14955