Raise RotatedTransformError for rotated GeoTIFFs

[brendancol]

Closes #2267.

Summary

• Replace the bare NotImplementedError in
  _geotags._extract_transform_and_georef with the typed
  RotatedTransformError, so rotated GeoTIFFs and rotated VRTs share
  one exception contract.
• Update the stale comment in _attrs.py:813 and the __init__.py
  docstrings that referenced the old error type.
• Update the four existing tests that asserted NotImplementedError
  on the rotated ModelTransformationTag path.
• Add test_rotated_typed_error_2267.py to pin the parity: parser
  raises RotatedTransformError, subclasses
  GeoTIFFAmbiguousMetadataError and ValueError, message still
  names the tag, and allow_rotated=True still reads the pixel grid.

Backend coverage

Read-path only (numpy + dask). No GPU code touched. Writers are not
affected; the existing drop_rotation plumbing in to_geotiff stays
as-is.

Test plan

• pytest xrspatial/geotiff/tests/test_rotated_typed_error_2267.py
  • new tests pass
• pytest xrspatial/geotiff/tests/test_allow_rotated_geotiff_2115.py xrspatial/geotiff/tests/test_geotags.py xrspatial/geotiff/tests/test_georef_status_2136.py xrspatial/geotiff/tests/test_remaining_fail_closed_1987.py xrspatial/geotiff/tests/test_ambiguous_metadata_hooks_1987.py xrspatial/geotiff/tests/test_http_dask_allow_rotated_2130.py xrspatial/geotiff/tests/test_backend_parity_matrix.py - all green
• pytest xrspatial/geotiff/tests/ - only pre-existing failure
  (test_lowlevel_write_pushdown_2138::test_write_vs_to_geotiff_byte_parity_uint8[lz4],
  unrelated lz4 experimental-codec gate) remains.

Compatibility note

RotatedTransformError is a ValueError subclass, so anything that
caught ValueError keeps catching the rotated case. Code that wrote
except NotImplementedError specifically for the rotated branch will
not catch it any more, which is the intentional half of the fix: that
contract was the bug.

[brendancol]

PR Review: Raise RotatedTransformError for rotated GeoTIFFs (#2272)

Blockers (must fix before merge)

None.

Suggestions (should fix, not blocking)

• Add a CHANGELOG.md entry under ### Unreleased. The repo lists
  one bullet per behaviour change with the PR number, and the original
  RotatedTransformError introduction already has a #1987-era entry
  there. This PR extends that typed error to the GeoTIFF entry point,
  so a sibling bullet referencing (#2267) keeps the breaking-but-
  intentional behaviour change visible to anyone scanning the
  changelog before upgrading. (CHANGELOG.md, top of ### Unreleased)

• Update the stale historical comment at _backends/dask.py:206.
  It still says rotated remote GeoTIFFs "raised NotImplementedError
  from _parse_cog_http_meta". Historically accurate for pre-#2130,
  but anyone grepping for the typed-error contract will land on it
  and be briefly confused. Either retype to RotatedTransformError
  while keeping the historical framing, or add a (now RotatedTransformError after #2267) parenthetical. Cleanup only.

Nits (optional improvements)

• test_extract_transform_rotated_does_not_raise_notimplemented
  at xrspatial/geotiff/tests/test_rotated_typed_error_2267.py:137-153
  is functionally identical to
  test_extract_transform_rotated_raises_typed_error just above it.
  RotatedTransformError does not subclass NotImplementedError (it
  inherits from ValueError), so the inner except NotImplementedError:
  clause is unreachable and the test reduces to
  pytest.raises(RotatedTransformError). Either drop it or rewrite
  it to assert not issubclass(RotatedTransformError, NotImplementedError),
  which actually pins the type-hierarchy contract the docstring
  claims to guard.

What looks good

• The exception swap at _geotags.py:684 keeps the original message
  text: tag name, coordinate term values, allow_rotated=True hint.
  No diagnostic regression.
• Tests hit both the unit surface (_extract_transform on a
  synthetic IFD) and the end-to-end surface (open_geotiff on a real
  on-disk rotated TIFF), and the existing #2115 / #2130 / #2136 /
  #2132 fixtures cover the dask and HTTP variants.
• The stale comment in _attrs.py:813-820 is rewritten, not just
  patched, so it now describes the symmetric contract instead of
  contradicting it.
• test_rotated_error_is_geotiff_ambiguous_subclass explicitly pins
  the GeoTIFFAmbiguousMetadataError and ValueError invariants,
  so the legacy except ValueError path is locked down.

Checklist

• Algorithm matches reference/paper - N/A, no algorithm change
• All implemented backends produce consistent results - GeoTIFF
  and VRT now share the typed error; dask and HTTP paths go through
  the same parser
• NaN handling is correct - N/A
• Edge cases are covered by tests - rotated + opt-in, rotated +
  default, axis-aligned passthrough; rotated + dask chunked; rotated
  • HTTP
• Dask chunk boundaries handled correctly - N/A (error path)
• No premature materialization or unnecessary copies - N/A
• Benchmark exists or is not needed - not needed (error-path
  change)
• README feature matrix updated (if applicable) - not applicable
• Docstrings present and accurate - __init__.py docstrings
  updated

[brendancol]

Follow-up review (after f02b607)

Disposition of the original review findings:

Suggestions

• CHANGELOG entry -- added under ### Unreleased next to the
  existing #1987 entry that introduced RotatedTransformError,
  describing the GeoTIFF parity extension and the breaking-but-
  intentional half (callers catching NotImplementedError
  specifically must switch to RotatedTransformError or
  ValueError).
• Stale comment at _backends/dask.py:206 -- updated with a
  (now RotatedTransformError after #2267) parenthetical, preserving
  the pre-#2130 historical framing.

Nits

• Redundant regression test -- rewrote as
  test_rotated_error_not_a_notimplemented_subclass, which uses
  issubclass to pin the type-hierarchy invariant directly. Also
  pins the inverse (NotImplementedError is not a
  GeoTIFFAmbiguousMetadataError) so accidental hierarchy drift in
  either direction fails loudly.

All 6 tests in test_rotated_typed_error_2267.py still pass; the
rotated-related fixtures across test_allow_rotated_geotiff_2115,
test_http_dask_allow_rotated_2130, test_georef_status_2136,
test_backend_parity_matrix, test_geotags, and
test_ambiguous_metadata_hooks_1987 are unchanged and green.