Refactor filament change to support multiple AMS units

[synman]

Context

TODO comment in src/bpm/bambuprinter.py:627 indicates the filament change logic needs refactoring to support multiple AMS units.

Current Behavior

Filament change assumes a single AMS unit.

Expected Behavior

Support multiple AMS units during filament change operations.

Related

• AMS mapping generally doesn't work and definitely not like BL intended #8 (AMS mapping) — related AMS handling issue

References

• src/bpm/bambuprinter.py:627

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Created from workspace-wide TODO audit.