Update all disassembly code to use new cgo-based decoder API with
stack-allocated instruction structs instead of heap-allocated
pointers. Add instruction filtering to skip decoding operations that
register tracking doesn't care about, avoiding expensive CGo calls.
Key changes:
- Replace Decompose with DecomposeInto using stack allocation
- Add mayBeTrackedInstruction filter for common tracked ops
- Introduce helper functions for safe operand/register access
- Fix metaclass pointer index to use caller index for efficiency
- Remove root file special-casing in pointer index builder
- Add comprehensive unit tests for tracking options and helpers
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