fix: honor log_level=DEBUG for the meshcore library logger

[sg]

Problem

Setting log_level = DEBUG in mcbot.conf enabled the bot's own debug lines but NOT the meshcore library's verbose output; only --debug produced the library firehose. (Confirmed from a live log: the startup banner showed logging at DEBUG (log_level=DEBUG) and a [DEBUG] line from the mcbot logger appeared, while the meshcore logger stayed quiet.)

Root cause

MeshCore.__init__ sets the meshcore logger level from its debug argument (debug=True → DEBUG, else → INFO) — and that arg is only a logger-level switch, nothing else. The bot calls create_serial(..., debug=self.cfg.debug) during run(), after setup_logging. So:

1. setup_logging sets meshcore → DEBUG
2. create_serial(debug=False) at connect overrides it back to INFO

--debug worked only because it set cfg.debug=True, making the library set its own logger to DEBUG.

Fix

• Add effective_log_level(cfg) (DEBUG if --debug, else log_level).
• run() passes debug=want_debug (from the effective level) to create_serial/create_tcp, and re-asserts the meshcore logger level immediately after connecting — covering the TypeError fallback path and WARNING/ERROR (which the library would otherwise floor at INFO).
• setup_logging uses the same helper.
• Regression test reproduces the override-then-reassert sequence and checks effective_log_level.

Testing

py_compile clean; tests/test_logging.py, tests/test_repeat_tracking.py, tests/test_radio_eviction.py all pass. With this, log_level=DEBUG yields the full library [DEBUG] output (e.g. Received RF log data: …) without --debug.

Note

Supersedes the logger-level portion of #10 (which set the level in setup_logging but was overridden by the library at connect). The #11 startup banner is what made this diagnosable from the live log.