A check's summary, test row and error line are cut with `clip`, so a failing test named with an emoji reads whole #6629

Intent: the lines a red check is explained by use src/text/clip.ts instead of their own cut.

Done:

• [ ] src/checks/words.ts, src/checks/tests-row.ts, src/checks/summary.ts and src/runs/error_line.ts each call clip, and their own cut code leaves.
• [ ] A test gives error_line a 300-character line with an emoji straddling its limit and finds no lone surrogate. It fails on main.
• [ ] The tests that import these four modules pass.

Files: src/checks/words.ts, src/checks/tests-row.ts, src/checks/summary.ts, src/runs/error_line.ts, test/text-clip-checks.test.ts