Refactoring and new Features

[TitusLabs]

Summary

This PR modernizes klipper_z_calibration around three goals:

1. make Klipper/Kalico compatibility assumptions explicit and testable,
2. improve installation, update, release, and validation workflows,
3. make the calibration offset application more flexible for toolchanger-style printers.

The runtime behavior of the normal calibration flow is intentionally kept close to the existing plugin: CALIBRATE_Z still measures nozzle, switch and bed positions, validates the calculated offset against offset_margins and applies the result. The larger change is that Klipper/Kalico API access is now isolated behind compatibility helpers and covered by unit and firmware-contract tests.

User-Visible Changes

• Adds support for configurable offset application through offset_gcode.
  • If unset, the plugin keeps the existing SET_GCODE_OFFSET behavior.
  • If set, the calcualted offset is passed as params.Z to the configured G-Code template.
  • This allows multi-head, IDEX and toolchanger configurations to route the calculated adjustment through printer specific macros.
• Adds optional error_gcode.
  • If configured, it runs when CALIBRATE_Z raises an error.
  • The original error is still raised after the hook runs.
  • The error text is passed as params.ERROR.
  • If error_gcode itself fails, that failure is logged without masking the original calibration error.
• Removes legacy configuration names older two years from the current documented configuration path:
  • max_deviation is replaced by offset_margins.
  • clearance is replaced by safe_z_height.
• Updates the README with the current support scope, install notes, Moonraker update behavior and compatibility guidance.

How to Test

In the Moonraker config change the primary_branch to testing/z-calibration-refactor and channel to dev:

[update_manager z_calibration]
primary_branch: testing/z-calibration-refactor
channel: dev
...

How to Revert

Remove the primary_branch in the Moonraker config and change the channel to stable.