Components had a single caller, which only ever fed it the bounds of the image
it then passed to Encode. Exporting it gave callers two ways to get it wrong —
components mismatched with the image, or out of the 1..9 range — in exchange for
a knob nobody turned.
Derive them from img.Bounds() at the top of Encode and unexport the helper. The
counts must come from the pre-downscale bounds: downscale's integer rounding can
shift the ratio across a component boundary, and the hash is a client-side cache
key. Verified byte-identical over 18 hashes spanning 9 aspect ratios.
The out-of-range validation goes with it, being unreachable once the counts are
always derived. The aspect-ratio table now asserts through Encode's size flag,
which encodes (x-1)+(y-1)*9.
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