tools/dm_xref.py extracts all DM address references from PM code
and shows the actual DM contents at those addresses:
- I-register loads with matching L-register buffer lengths
- Direct DM(addr) reads and writes
- CNTR loop counters
- Hex, decimal, and Q15 format for DM content
- Automatic detection of uninitialized (zero) regions
- Configurable context window (--context N words)
