Re-scan at finer granularity: collision..moby is entirely texture

The "3 of 21 blocks not texture-like" figure from the last commit was an
artifact of sampling every 256 KB and missing everything between. Re-scanned
at 4 KB granularity there are about 100 such blocks, and looking at them
rather than only counting them, they are smooth gradient ramps -- sky and
fog texture. A noisy gradient has a high distinct byte count without being
code, which is exactly the mistake the byte-count heuristic invites.

So collision..moby is entirely texture data. There is no separate moby_anim
region there, and two claims about this range have now been wrong: the
"6.2 MB of unknown data" and the "3 unexplained blocks". Both came from
sizes and counts taken without looking at what they described.

moby_anim is therefore still unlocated, but it is not here. The remaining
candidate is the unresolved tail after the last shrub class -- ~925 KB of
real, non-zero data on level 0 that nothing accounts for.

Recording the two corrections together rather than one at a time, because
the mechanism is the same in both: a heuristic count is not an
identification.

docs/formats/core-data-regions.md

@@ -86,5 +86,18 @@ The texture table's `data_offset` values only reach 5326208, which is why the
 gap looked real: mip chains extend well past the last entry's offset. A region
 sized from a table of first-level offsets understates the data it points at.
 
-Three of the 21 sampled blocks are not texture-like, so something is mixed in
-and is not yet identified, but it is not 6.2 MB of `moby_anim`.
+The "3 of 21 blocks not texture-like" figure in the previous revision was an
+artifact of sampling every 256 KB. Re-scanned at 4 KB granularity the whole
+range is texture data: ~100 blocks stand out, and looking at them they are
+smooth gradient ramps -- sky and fog texture, exactly what gradient texels look
+like. A noisy gradient has a high distinct byte count without being code.
+
+So the range between collision and moby is **entirely texture data**, and there
+is no separate `moby_anim` region there. Combined with the correction above,
+two claims made about this range have now been wrong: the "6.2 MB of unknown
+data" and the "3 unexplained blocks".
+
+Where `moby_anim` actually lives is therefore still open, but it is not here.
+The remaining candidate is the unresolved tail after the last shrub class,
+which on level 0 is ~925 KB of real, non-zero data that nothing yet accounts
+for.