Add diffRanges offset-tuple API, finalize 1.1.0 changelog

[krkarma777]

Summary

• New diffRanges(a, b, options?): returns changed regions as [aStart, aEnd, bStart, bEnd] UTF-16 code-unit offset tuples — the projection of diff() entries onto string offsets, for editors/highlighters that slice the originals themselves; composes with mode/refine/heuristic
• CHANGELOG: [Unreleased] finalized as [1.1.0] including the hosted demo and heuristic/refine entries
• README API section documents diffRanges and the diffTokens options argument

Test Plan

• 4 new tests incl. 2,400-case fuzz: ranges ascending/non-overlapping, no empty-empty tuples, and splice-rebuild of b from a across all modes × refine on/off
• Full suite 43/43, typecheck clean