FakeSerial Marlin Coverage

FakeSerial uses Marlin.php as the command inventory.

Behavior rules:

Every command listed in Marlin.php now routes through an explicit FakeSerial behavior path.
Stateful commands mutate emulator state so future printer-state inspection can rely on coherent machine data.
Hardware-limited commands return coherent device-specific failures instead of generic unknowns.
Commands not present in Marlin.php still return Error:Unknown command.

Current coverage model:

Motion and positioning: linear moves, arc-like moves, dwell, units, homing, workspace selection, stored positions, retract / recover, parking
Probe, leveling, calibration, backlash, and homing-offset families
SD card lifecycle, selection, logging, progress, sorting, abort, and print-timer families
Power, steppers, spindle / laser, coolant, blower, fans, lights, LCD, tone, camera, and servo families
Temperature, PID, waiting, auto-report, material preset, and chamber / cooler temperature families
Filament, runout, width sensing, filament change, loading / unloading, and extrusion tuning families
EEPROM-style save / restore / validate / report families
Security, passcode, macro, prompt-response, network, and maintenance families
Driver, TMC, stepper-current, microstepping, kinematics, SCARA, Delta, and diagnostic families

Notable coherence guarantees:

Tool selection respects the fake printer’s single-extruder limit. Example: T7 returns a tool-unavailable error.
MMU-only Tx commands return an explicit MMU-unavailable error.
Bare-command smoke testing across the full Marlin.php inventory now produces no Unknown command or Unsupported FakeSerial command responses.

Verification: