Parse flush multiplier and adjust flush matrix accordingly to match Orca and Bambu requested purge volumes

[igiannakas]

As I was experimenting with Blobifier I noticed that the purge matrix was not changing as the flush multiplier was increased or decreased in Orca slicer as I was trying to validate this Orca slicer PR I've raised here: SoftFever/OrcaSlicer#7508

For example:
Multiplier of 1.2

Gcode file:

Multiplier of 0.5

Gcode file:

This results in an incorrect purge matrix being sent to the blobifier for use when purging that does not match the intended action from the user in the UI. Instead the purge matrix is always as if 1.0 multiplier was set in the UI.

This happens because both Orca and Bambu generate a base purge matrix and a separate multiplier and they output both to the gcode for use by Happy Hare etc. To calculate the effective purge volume, these two values need to be multiplied so they match the user intent.

This PR proposes to parse the flush multiplier and apply it to the purge matrix before use in the placeholder variables.

Results:
For example, now with a 0.5 multiplier the purge volumes correspond to what the UI displays