Optimisation: ERS - Reduce redundant gcode commands from extrusion rate smoothing

[igiannakas]

Extrusion rate smoothing (pressure equaliser) materially increases gcode size due to significant redundancies in the produced gcode.

This PR aims to reduce this, making the gcode smaller and hence, more easily printable due to reduced gcode commands / second issued to the printer.

The changes in this PR:

1. Address a bug where even 0 change in flow rate would result in a line split
2. Filters out inconsequential variances in flow rate (less than 5mm/sec speed for a 0.25 mm nozzle) which would have otherwise led to increased line splitting for no visual gain, as the flow delta is insignificant.

Examples:

ERS splits continuous straight lines to segments irrespective of extrusion rate smoothing being applied or not.

This PR fixes this - lime splitting is significantly reduced:

Total Gcode volume reduction:
Before: - 157169 lines for the test cube
After: 65199 lines for the test cube

2.4x gcode volume reduction.
This gcode volume reduction should also help reduce stuttering in the visual preview of the model as the UI rendering is now much lighter.

Tests:
No regressions observed.

Before:

After: