elm327.py swallows errors with bare except Exception (4 sites)

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carwatch/elm327.py lines 95, 146, 241, 254 (verified): bare except Exception: with no logging. OBD dongles vanish mid-drive as a rule; at least log at debug level so a field trace is possible. From @Hermes's review, 31 Aug.

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Accurate count from the current main (superseding both earlier counts): 10 broad except Exception sites total — 6 bare/silent (lines 95, 146, 241, 254, 568, 613) and 4 catching as e (413, 555, 615, 661) whose logging should be checked too. Consolidating: #22 filed the same finding in parallel and is closed as a duplicate of this one.