Maximum volumetric flow rate, with fixes

[ghost]

Description

This PR adds functionality for setting a maximum volumetric flow rate, which prevents hitting the limit at which a certain hotend can melt material.

This PR attempts to fix the compilation errors in #1814

/home/runner/work/CuraEngine/CuraEngine/src/LayerPlan.cpp:2129:23: error: assignment of read-only variable ‘extrude_speed’
 2129 |         extrude_speed *= max_mm3_per_sec / mm3_per_sec;

It contains the commit from #1814 and therefore all necessary changes to CuraEngine.

It goes with #14452 on Cura, which adds the required settings to the frontend.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Compiled flawless.

The preview clearly shows that the flow and speed get limited if the maximum flow rate is reached:

With maximum set to 0.0mm³/s (disabled):

With maximum set to 5mm³/s:

Test Configuration:

• Operating System:
  Arch 6.1.10 Wayland/KDE

Checklist:

• My code follows the style guidelines of this project as described in UltiMaker Meta
• I have read the Contribution guide
• I have commented my code, particularly in hard-to-understand areas
• I have uploaded any files required to test this change

[mjc-506]

Thanks for 'updating' the PR and sorry for the very slow response! There does appear to have been a change to const variables at some point between submitting my original PR and the tests being run... I'll consider that 'lucky' haha