fix: preserve component sample model band offsets

[ShiroKSH]

Summary

• pair ComponentSampleModel band offsets with band positions in its contiguous fast path
• add coverage for a legal raster layout that reorders data banks and uses distinct offsets

The slow path already uses the band position. The fast path used the mapped bank number instead, returning samples from the wrong positions when the mapping is non-identity.

Validation

• executed the regression fixture against the updated fast-path implementation
• ran Python bytecode compilation
• ran Black formatting verification
• checked the staged diff with git diff --check

[jiayuasu]

One question on the offset handling.

[jiayuasu]

Could we calculate the effective start here (data_buffer.offsets[bank_index] + self.band_offsets[k]) and always slice a width * height window? I may be missing an invariant, but a component model can have a zero band offset with a padded backing bank; then the current branch seems to pass the whole bank to reshape(). The slow path may need the buffer offset too. A zero-offset case in the new test would help confirm it.