New package com.elphel.imagej.gpu.testdata implementing the Java side of
tile_processor_gpu/src/tests/testdata_format.md:
- TestDataWriter: raw little-endian arrays + manifest.txt (prm/buf records)
- TestDataReader: parse manifest or C++ results back for ImageJ comparison
- AvgTdExport: full clt_average_sensors test case (per-sensor TD from
  GpuQuad, CuasTD.consolidateSensorsTD expected outputs + counts, optional
  TpTask per-sensor XY for the OOB stage) + compareResults round-trip check

Round-trip verified bit-exact (max|diff|=0): TestDataWriter -> CUDA
test_avg_td on GPU -> TestDataReader.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>