Soften incorrect packbits-only-uint8 claim in test commentary

Copilot flagged the docstring and section comment claiming packbits in
this writer only supports uint8. packbits operates on the raw byte
stream, so any dtype is technically supported; uint8 is just the variant
this test exercises (and the dtype packbits was designed for).

Author: brendancol

xrspatial/geotiff/tests/test_streaming_codecs_2026_05_11.py

@@ -9,8 +9,10 @@
 * Dask streaming write + LERC (lossless and lossy ``max_z_error``)
   produces identical output to the eager writer.
 * Dask streaming write + LZ4 round-trips a float32 raster.
-* Dask streaming write + packbits round-trips a uint8 raster (the only
-  dtype packbits supports in this writer).
+* Dask streaming write + packbits round-trips a uint8 raster. packbits
+  operates on the raw byte stream so any dtype is technically supported;
+  uint8 is the variant exercised here and the one packbits was designed
+  for (run-length encoding of byte runs).
 * COG output with ``overview_resampling='cubic'`` round-trips through
   scipy.ndimage.zoom (the only overview method that takes a separate
   code path in ``_block_reduce_2d``).
@@ -139,7 +141,7 @@ def test_streaming_matches_eager(self, float_raster, dask_float_raster,
 
 
 # ---------------------------------------------------------------------------
-# packbits: round-trip on uint8 (the only supported dtype)
+# packbits: round-trip on uint8 (the dtype packbits is designed for)
 # ---------------------------------------------------------------------------
 
 class TestStreamingPackbits: