[gspark-etri]

Background

aicomp #129 asks the engine to switch a resident NPU build to another build of the same model by uploading only the changed parts. For that, the engine needs the changed byte ranges per file, and onggi diff reported only totals (#46).

Changes

• Store.Diff takes DiffOptions{Ranges}. With it, FileDiff.Changed lists the changed runs as [offset, length]; every other byte is at the same offset in the paired base file.
• CLI: onggi diff --ranges [--json].

Verification

• Unit test: the ranges are ordered, inside the file, equal in number to changed_runs, and cover exactly size - same; the bytes before the first range equal the base. Without the option, changed is absent.
• Lab store, decode B2 → decode B8 (15.2 GB .rbln):

changed decode_S256_B8_lm.rbln offset 0 length 45196 (45.2 kB)
changed decode_S256_B8_lm.rbln offset 60586 length 9212 (9.2 kB)
changed decode_S256_B8_lm.rbln offset 15009911429 length 218137453 (218.1 MB)

The first 70 KB and the last 218 MB differ; the 15.0 GB between them is identical at the same offsets. Formats are not parsed (ADR-0009); these are byte positions only.

Compatibility and limits

• Store.Diff gained a parameter (Go API). The CLI output is unchanged without --ranges.

Related Issue

Closes #46

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