Notes on ledger lines need extra horizontal side-clearance beyond in-staff notes of the same duration

A ledger line extends beyond the notehead on both sides (SMuFL's `engravingDefaults.legerLineExtension` is exactly this metric), and adjacent ledger-line notes need enough horizontal gap that their ledger lines don't visually merge or overlap another note's ledger lines.

No term in `fixedExtras`, `formatW`, or `NOTE_PAD` (line 829) references clef or pitch at all — ledger-line notes get IDENTICAL width to in-staff notes of the same duration. A passage with several consecutive far-below/above-staff notes (common once fugue subjects or bass-voice chorale lines range wide) can render with ledger lines nearly touching a neighbor's ledger lines, since nothing in the width math ever asks how many ledger lines a note needs.

SMuFL specification, `engravingDefaults.legerLineExtension`; Gould, Behind Bars (ledger-line spacing; Ross, The Art of Music Engraving (extra clearance around extreme-register notes); VexFlow's own `StaveNote.drawLedgerLines` (`node_modules/vexflow/src/stavenote.ts`, lines 1036-1099), which draws a ledger line only once a note is 2 diatonic staff-positions beyond the outer staff line (the immediately adjacent space gets no ledger), confirming the standard convention exactly.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.