bugfix: resolve 40+ crashes, threading races, and Klipper protocol issues

[gmmcosta15]

Select the type:

• Feature
• Bug fix
• Code refactor
• Documentation

This PR introduces the following changes:

Threading & concurrency (moonrakerComm.py):

• Move class-level state vars (connected/connecting/_reconnect_count/callback_table)
  into init to prevent shared state across instances
• Add _state_lock (RLock) and _request_lock guarding all reads/writes to those vars
• Fix mutable default dict in send_request (params={} → params=None)
• Fix unbound super() in OneShotTokenError (init without class arg)
• Guard _retry_timer with None before stopTimer/startTimer calls; stop existing
  timer in try_connection before creating a new one (prevents orphaned threads)
• sendEvent → postEvent for cross-thread event delivery
• Wrap json.loads in try/except; use .get() on all external response dicts
• Fix dest_dir guard (False → None) in copy/move file; fix machine.update.client
  missing params dict; fix machine.update.rollback method typo (comma → dot)
• Add klippy startup/disconnected retry cap (30 attempts) to prevent infinite loop
• Add join(timeout=self.timeout+1) on _wst to avoid indefinite block

RepeatedTimer: fix inverted stopEvent semantics (set=stop, clear=running)

Pi runtime crashes:

• cancelPage: fix AttributeError on file_metadata dict access
• connectionPage: fix stale slot name
• inputshaperPage: fix uninitialized currentItem reference
• mainWindow: fix _handle_notify (dict.popitem → next(iter(items())));
  fix global_back tab-bar gate; fix logger f-string
• filamentTab: fix slot signature mismatch; fix stale _is_printing state;
  fix bare self.isVisible reference (missing parentheses)
• jobStatusPage: use separate event_state var (never reassign lstate);
  capture file locals before clearing state; print_finish only on complete;
  layer fallback uses Mainsail ceil formula; layer_fallback flag decoupled
  from total_laye
• sensorsPanel: removeWidget+deleteLater before clearing tracking dict on
  reconnect to prevent widget stacking
• babystepPage: label sync with confirmed Klipper value, button reorder,
  code deduplication
• probeHelperPage: only process is_active when key present in update dict
  (Klipper sends position-only reensaver: guard DPMS calls with hasattr(_dpms_available) check

Python 3.11 typing (20 files):

• Opional/Union/List/Dict → native syntax; add from future import annotations
• filament.brand setter: return type None; _spool_type initialized in init
• files.py: remove duplicate ReceivedFileData import; use events.ReceivedFileData

helper_methods:

• convert_bytes_to_mb: remove spurious self param; rename bytes → size_bytes
• calculate_current_layer: Mainsail formula (ceil((z-first)/layer+1)), clamped
• calculate_max_layers: extracted from calculate_current_layer; max(1,...) guard
• normalize, check_filepath_permission, check_dir_existence: pathlib + type hints
• estmate_print_time: modernized variable names and return type annotation
• Remove unused get_file_loc/digest_hash stubs; remove normalize import from
  controlTab and tunePage

controlTab/tunePage slider split:

• controlTab.on_slider_change: handles fan_generics only (SET_FAN_SPEED)
• tunePage: _on_speed_slider_change for print speed (M220) and on_slider_change
  for fan_generics — eliminates collision when fan is named speed

Motivation

• Fix 40+ bugs causing crashes, UI freezes, and incorrect state on Pi hardware, including thread-race conditions in the WebSocket layer, bad event dispatch between threads, and incorrect Klipper protocol handling
• Modernise Python typing across 20 files (Optional/Union/List/Dict → native 3.11 syntax) and clean up helper_methods.py (spurious self, shadow of bytes builtin, Mainsail-ported layer formulas)
• Split fan/speed slider callbacks in controlTab and tunePage to eliminate gcode dispatch errors when a fan_generic is named "speed"

[gmmcosta15]

Separate this changes into a new PR