feat(Preheat): add chamber temperature (M141) support to preheat gcode

[meteyou]

Description

This PR adds chamber temperature support to the preheat gcode button. When a G-code file contains chamber_temp metadata (from slicers like PrusaSlicer), the preheat button will now also send M141 S<temp> to set the chamber temperature.

Key implementation detail: The M141 command is only added if Klipper reports M141 as an available G-code command. This ensures backward compatibility with printers that don't have a chamber heater macro configured. Example for a M141 macro:

[gcode_macro M141]
gcode:
    SET_HEATER_TEMPERATURE HEATER=chamber TARGET={params.S|default(0)|float}

Related Tickets & Documents

• fixes Activate and enter the Active/Passive temperature control of the Chamber using the Mainsail PREHEAT button. (M141 and M149). #2367

Mobile & Desktop Screenshots/Recordings

n/a

[Copilot]

Pull request overview

This PR adds chamber temperature support to the preheat gcode functionality by enabling the M141 command to be included in preheat gcode when the file metadata contains chamber_temp and the printer supports the M141 command.

Key changes:

• Added M141 (chamber temperature) to the list of supported preheat commands
• Implemented dynamic filtering to only include preheat commands that are available in Klipper's gcode.commands
• Moved the preheat_gcode_objects definition outside the file iteration loop for better performance

[escodacarles]

It's amazing! thank you!