Fix truncation exceeding maxWidth for wide characters

[RyogaK]

Summary

• Fixes Truncation exceeds maxWidth for East Asian wide characters #28 — cliTruncate output exceeds columns when the truncation boundary falls inside an East Asian wide (CJK) character
• Adds safeSliceAnsi wrapper that re-slices with a 1-column narrower range when sliceAnsi rounds up
• Applied to all three positions (end, start, middle)
• Workaround for sliceAnsi returns wider result than specified endColumn for wide characters chalk/slice-ansi#43

Test plan

• Added test that verifies stringWidth(result) <= maxWidth for all widths 1–25 across all three positions with CJK input
• All existing tests pass

[RyogaK]

CI failure is unrelated to this PR — xo now flags @typescript-eslint/no-unnecessary-type-arguments in index.test-d.ts, which exists on main as well. Likely a newer xo or typescript-eslint version in CI picked up the rule.

[RyogaK]

Opened #30 to fix the xo lint error.

The main branch itself is currently failing CI due to a transitive dependency issue (see #31). @sindresorhus could you address that first when you get a chance? This PR's CI can't pass until then.