Inheritance was overkill here, and now we can use inheritance for new functionality X
without having to create classes for all combinations of {X, is_testnet}.
As opposed to using TestCaseForTestnet class, this allows having a single class
of many related unit tests, some using testnet and some using mainnet constants.
Previously, during early-startup (until configure_logging(config) is
called in run_electrum),
- the stderr log handler lost all log messages below warning level, and
- the file log handler lost all log messages regardless of log level
We now instead start buffering log messages in memory as soon as
electrum.logging is imported. The buffer is dumped into the
stderr and file log handlers when they are fully set up, and then
the buffer is discarded (and the temporary log handler is removed).
Note that messages are not logged until configure_logging() is called.
Previously WARNING/ERROR messages would get logged immediately to stderr,
but not anymore. This was changed so that the order of the log messages
can be kept intact. (if we log WARNINGs immediately, but need to delay
INFOs until the config is available, messages would either be out of order
or alternatively there would be duplicates)
Relatedly, we now follow the recommendation of the python docs re
logging for libraries [0]: we try to only configure logging if running via
run_electrum (the main script) and not when e.g. a 3rd party script
imports electrum.
[0]: https://docs.python.org/3/howto/logging.html#configuring-logging-for-a-library
The few other cases that used SimpleConfig.get_instance() now
either get passed a config instance, or they try to get a reference
to something else that has a reference to a config.
(see lnsweep, qt/qrcodewidget, qt/qrtextedit)
