Add multiACE source-change timing and print statistics

[physicsG]

Summary

Extend the print-time and material accounting pipeline so multiACE source swaps are tracked separately from U1 physical tool changes and reflected in preview estimates.

Scope

• Add a source-change event/category to the G-code processor.
• Track source-change count and accumulated time separately from physical head changes.
• Add configurable timing components for unload, tip forming, route change, load, verification, and expected retry allowance.
• Attribute purge and material usage correctly to outgoing and incoming filaments.
• Reconcile generated source-change commands with estimated event counts.
• Expose a preview breakdown for base motion, tool changes, source swaps, purge, temperature overhead, and total estimate.
• Allow future printer-measured route timings to override profile defaults.

Proposed code areas

src/libslic3r/GCode/GCodeProcessor.cpp
src/libslic3r/PrintConfig.hpp
src/libslic3r/PrintConfig.cpp
src/libslic3r/PresetBundle.cpp

Acceptance criteria

• Physical tool changes and source swaps are counted independently.
• Estimated source-swap time is configurable by profile.
• The estimate includes unload, route, load, verification, and retry allowance.
• Purge time and purge material are not double-counted.
• Generated G-code source-change count matches the estimator event count.
• Preview displays a clear timing breakdown.
• Missing measured timing falls back to profile defaults.
• Unit tests verify timing formulas and boundary values.
• Integration tests reconcile preview totals against generated command sequences.

Dependencies

• Depends on Generate native multiACE source-change G-code for the U1 #3 for native source-change events.
• Uses routing information from Add persistent filament-source and U1 toolhead routing model #2.

Design references

• doc/multiace_u1_integration_design.md
• doc/multiace_testing_strategy.md