000b2c7d4a755547ebea3a61259d6d5c1e3c81b3  Unreviewed, address unexpected safer cpp issue on the bots

Classified as not security-relevant.
Triage note: Replaces `auto& rootStyle = root->style()` with `CheckedRef` and wraps `style.fontCascade()` in `protect()` in blockEllipsisForLine/hangablePunctuationEndWidth. Pure static-analyzer (CanMakeCheckedPtr) hardening with no behavior change and no concrete lifetime bug shown in the diff.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+3.0), clamp_saturate (+1.8), area:Source/WebCore/layout (+2.0), surgical (+1.3)