Let the flashlight respect on_expander and expose LEDC channels

[pascalzauberzeug]

Motivation

FlashlightHardware ignored on_expander and prefixed the Lizard PwmOutput with the expander name whenever an expander was passed, regardless of the flag.
It also hard-coded the LEDC channel allocation, which can collide with other PwmOutputs on the same chip — see #33.

Implementation

• Respect on_expander: the expander prefix is only applied when both an expander is present and config.on_expander is true.
• Make LEDC allocation explicit: expose ledc_timer, front_ledc_channel, back_ledc_channel on FlashlightConfiguration and pass them as the second/third argument to PwmOutput(...).
  Defaults match the previous implicit allocation (timer 0, channels 0/1).
• Make brightness configurable via duty_cycle (0.0–1.0), converted to the 8-bit Lizard duty value; previous behavior (full brightness) is preserved as the default.

A docstring note reminds users that the LEDC channels must not collide with other PwmOutputs on the same chip.

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• I chose meaningful labels (if GitHub allows me to so).
• I documented breaking changes and set the 'breaking change' label if needed
• The implementation is complete.
• Tests with a real hardware have been successful (or are not necessary).
• Pytests have been added (or are not necessary).
• Documentation has been added (or is not necessary).