[jpegli] fix buffer overflow when chroma component has refinement

[haixia-meta]

See issue 14 for context.

Under certain conditions, num_refinement_bits is computed wrongly causing a heap-buffer-overflow in jpegli's TokenizeACRefinementScan in https://github.com/google/jpegli/blob/main/lib/jpegli/entropy_coding.cc#L255

The problem seems to be function TokenizeJpeg which only has a single 1D array int num_refinement_scans[DCTSIZE2] to keep track of number of refinement passes for each DCT coefficient. This is inadequate when multiple color components have different refinement sequences.

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