fix(buffer): copyCellsFrom metadata scope and reflow isWrapped cleanup

[Tyriar]

Cherry-picks from Tyriar/explore-correctness (commits 992cc5c, cd4da10d), with a small merge adaptation on master for _copyCellMapsFrom.

1. BufferLine.copyCellsFrom — limit combined/extended metadata to copied range

copyCellsFrom copied Uint32 cell data only for the requested column range, but previously migrated every _combined entry with key >= srcCol. Partial line copies during reflow and wraparound could therefore attach grapheme metadata to unrelated destination columns.

Fix: Copy combined and extended attributes only per cell in the copied range, and delete stale entries on the destination when the source cell does not use them. On current master, this is implemented by extending _copyCellMapsFrom (used by copyCellsFrom and copyFrom) to clear stale _combined / _extendedAttrs keys when flags are absent.

Risk: Any path that partially copies cells between lines (reflow, wraparound, scroll regions).

Tests: BufferLine.test.ts — copyCellsFrom / should only move combined data within the copied range.

2. reflowLargerGetLinesToRemove — clear stale isWrapped after larger reflow

When widening the terminal unwraps a multi-row soft wrap and removes trailing buffer lines, the last retained row could still have isWrapped set, and the following line could still think it continued a removed row. That broke wrapped-range string translation.

Fix: When rows are removed during reflow, clear isWrapped on the last retained row in the group (wrappedLines[destLineIndex]) and on the first line after the group if present.

Risk: Resize/reflow and any feature that depends on correct wrap continuation across buffer lines (search, selection, translation).

Tests: BufferReflow.test.ts — reflowLargerGetLinesToRemove / should clear isWrapped on the last retained row after unwrap, plus existing cursor/reflow guard tests on master.

Verification

npm run build && npm run esbuild
npm run test-unit -- **/BufferLine.test.js
npm run test-unit -- **/BufferReflow.test.js