Add clustered GCode support

[MitchBradley]

Summary

• add support for colon-delimited clustered S values on linear moves
• expand clustered moves into internal linear sub-segments so the existing spindle and planner pipeline can be reused
• advertise support through $I as [CLUSTER:16]
• add parser coverage for clustered syntax

Notes

• This is intended for compatibility with senders that emit clustered laser power samples on linear moves.
• Longer background and wiki-style draft documentation: https://gist.github.com/MitchBradley/0684e8b3c15d60492de93aa69cd33e0b

[Copilot]

Pull request overview

Adds support for colon-delimited “clustered” S values on G1 linear moves, intended to allow senders to provide multiple spindle/laser power samples for a single move while reusing the existing planner/spindle pipeline.

Changes:

• Parse S words of the form S1:2:3... and gate them to linear motion blocks.
• Expand clustered G1 moves into multiple internal linear sub-segments with per-segment spindle_speed.
• Advertise capability via $I build info as [CLUSTER:16] and add parser coverage for the new syntax.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
FluidNC/src/tests/parser.nc	Adds a clustered-S G1 test line.
FluidNC/src/tests/parser-result.txt	Updates expected parser output to accept clustered syntax.
FluidNC/src/Report.cpp	Advertises clustered support in build info ([CLUSTER:16]).
FluidNC/src/MotionControl.h	Declares mc_clustered_linear_move(...).
FluidNC/src/MotionControl.cpp	Implements clustered move expansion into sub-segments.
FluidNC/src/GCode.cpp	Parses clustered spindle speed syntax and routes linear moves through clustered expansion.

Comments suppressed due to low confidence (2)

FluidNC/src/GCode.cpp:304

• gc_execute_line() introduces std::vector for clustered_spindle_speeds. When clustered syntax is used this will allocate from the heap in the hot G-code parsing path, which can increase latency and fragment memory on embedded targets. Consider using a fixed-capacity container (e.g., std::array + count, or a small-vector with an inline buffer) sized to the supported cluster maximum.

    bool laserIsMotion        = false;
    bool nonmodalG38          = false;  // Used for G38.6-9
    bool isWaitOnInputDigital = false;
    std::vector<float> clustered_spindle_speeds;

FluidNC/src/GCode.cpp:870

• When clustered S syntax is present, gc_block.values.s is set to clustered_spindle_speeds.back(). For non-rate-adjusted spindles, Step 4 may sync and apply this (last) S value before motion starts, so the move begins at the wrong spindle speed/power. Consider either restricting clustered S to rate-adjusted (laser) spindles, or applying the first clustered value before motion and only updating the modal spindle_speed state to the last value after the segmented move completes.

                        if (line[pos] == ':') {
                            if (!parse_spindle_speed_cluster(line, pos, value, clustered_spindle_speeds)) {
                                return Error::BadNumberFormat;
                            }
                            gc_block.values.s = clustered_spindle_speeds.back();