feat: rework diff helpers

.changeset/diff-rework.md

@@ -0,0 +1,11 @@
+---
+'@fuzdev/fuz_util': minor
+---
+
+Rebuild `diff.ts` around greedy Myers (breaking):
+
+- `diff_lines` replaces the LCS table with greedy Myers over interned lines — linear memory, common prefix/suffix trimming, and a `max_cost` cap that degrades gracefully to a replace block on unrelated inputs. Changed regions are normalized to removes-before-adds.
+- `DiffLine` gains 1-based `a_line`/`b_line` and `no_newline` (git's "no newline at end of file" semantics, no phantom empty final line); `line` is renamed to `text`.
+- New `diff_hunks`/`DiffHunk` group changes with context, replacing `filter_diff_context` and its `'...'` sentinel line.
+- New `diff_segments` computes intra-line changed-character ranges for paired remove/add lines, with a similarity gate.
+- `format_diff` takes hunks and emits unified-diff `@@` headers; colors now go through `print.ts`'s `st` seam (`use_color` removed).

CLAUDE.md

@@ -64,6 +64,10 @@ fuz_util is a **foundational utility library**:
   without rebalancing (`fractional_index_between`,
   `fractional_indices_between`; base62 alphabet, helper-side jitter,
   `FRACTIONAL_INDEX_REGEX` / `_LENGTH_MAX`)
+- `diff.ts` - line + intra-line char diffs via greedy Myers (`diff_lines`
+  with 1-based line numbers and `no_newline`, `diff_hunks` context grouping,
+  `diff_segments` changed-char ranges, `format_diff`/`generate_diff`
+  unified-diff text with `@@` headers)
 
 ### Async and timing