Add per-tool nozzle temperature control to CAL_Z

[kilene001-bit]

Summary

• add optional NOZZLE_TEMP and SOAK parameters to CAL_Z
• heat each passive tool only after pickup, so every nozzle is measured at the same requested temperature
• switch the heater off after measuring each tool and before it is parked
• preserve the existing cold CAL_Z behaviour when NOZZLE_TEMP is omitted
• document the command and hot-probing precautions

Example:

gcode CAL_Z NOZZLE_TEMP=150 SOAK=10

The bed heater is intentionally not controlled. CAL_Z measures the tools at the same XY location, while heating the bed adds stabilization time and another source of drift without being necessary to equalize the individual nozzle temperatures.

Motivation

The passive tools cannot be preheated while parked. Heating once at the beginning of CAL_Z therefore does not put subsequently picked tools into the same thermal state. This change waits for each attached nozzle individually before probing it.

On the test printer, the measured relative Z difference changed by about 0.025 mm between cold and 200 C nozzle measurements, which is significant for first-layer calibration.

Validation

Tested on a six-tool Bondtech INDX installed on a Voron Trident 350:

• bed unheated
• nozzle target 200 C
• 30 second soak per tool
• two consecutive complete six-tool runs
• every pickup and park completed successfully
• heater was switched off before each park and all heaters were off at completion

The documented 150 C example follows the temperature previously suggested for CAL_Z in the discussion on #36.