Type-check the full tconnectsync package

[jwoglom]

Remove the single-file opt-in in setup.cfg ([mypy] files) so mypy checks the entire tconnectsync package, and fix everything that surfaced.

Config:

• setup.cfg: mypy files now points at the whole tconnectsync package.

Event processors (were typed as BaseEvent, which lacks the per-event fields like seqNum and the event-specific attributes):

• Type each *_to_nsentry / helper with the concrete event type(s) it handles (or a Union of them), matching the existing process_alarm.py pattern.
• process_basal_suspension, process_basal_resume, process_cgm_start_join_stop: filter out None before appending to ns_entries, matching process_basal / process_cgm_alert. Previously a None from a non-matching event would have been appended and passed to upload_entry().
• Add explicit return None fall-throughs where a helper annotated to return a value could implicitly return None.
• process_cgm_reading: give each sensor's GlucosevaluestatusEnum its own local variable so the enum types don't clash.

process.py:

• Add an EventProcessor Protocol and annotate event_classes with it, so the instantiated handlers are typed instead of object.
• Rename the updater-loop variable so it no longer collides with the processor-loop variable's type.

Other:

• api/tandemsource.py: narrow the JWKS key to RSAPublicKey before jwt.decode, and use arrow.get() (not time.time()) when forcing token expiry so the attribute type stays consistent.
• api/common.py: split_days_range returns Arrow tuples, not str tuples.
• parser/nightscout.py: sort profile segments by the typed startTime rather than an untyped dict value (same resulting order).
• domain/tandemsource/pump_settings.py: PumpSettings inherits DataClassJsonMixin so from_dict is visible to the type checker.
• domain/tandemsource/event_class.py: ignore the set/Enum hash clash.
• nightscout.py: explicit return None when a ConnectionError is swallowed.

No runtime behavior change; full test suite (461 passed, 1 skipped) still green.