feat(table): draw row separators when any body row wraps

[denolfe]

Tables with wrapped cells get a horizontal rule between every body row. Single-line tables render as before.

Before:

│ MeshAnything V2 │ S-Lab 1.0 "for non-commercial purpose"; HF card │ no   │
│                 │ says MIT                                        │      │
│ MeshFlow        │ FAIR Noncommercial "will not use any outputs    │ no   │
│                 │ or results in connection with any commercial    │      │
│                 │ uses"                                           │      │

After:

│ MeshAnything V2 │ S-Lab 1.0 "for non-commercial purpose"; HF card │ no   │
│                 │ says MIT                                        │      │
├─────────────────┼─────────────────────────────────────────────────┼──────┤
│ MeshFlow        │ FAIR Noncommercial "will not use any outputs    │ no   │
│                 │ or results in connection with any commercial    │      │
│                 │ uses"                                           │      │

Key Changes

• Row separators for wrapped tables
  • The table wraps every cell once and checks whether any body row spans more than one line. If so, it inserts the existing mid rule between adjacent body rows.
  • Dense single-line tables keep only the header rule. This keeps compact tables compact.
• Row receives pre-wrapped lines
  • The separator decision is table wide, so the wrapping moved from each row to the table. Rows no longer wrap their own cells.

[github-actions]

Startup benchmark (--render test/exhaustive.md, linux-x64)

build	mean	ratio	verdict
baseline (main@02c86b3)	360.4ms ± 5.8ms	—
PR	358.6ms ± 6.0ms	1.00×	✅ ok

Thresholds: warn ≥ 1.1×, fail ≥ 1.25×. Baseline built from main.