Automatic re-barring: carry an over-full bar's overflow into the next measure

[alessonqueirozdev-hub]

What exists now

As of the fix that came with this issue, an over-full bar is reported:

Measure 1 holds 1.2500 whole notes in voice 1 but 4/4 allows 1.0000 —
an excess of 0.2500. The music was imported as written; nothing was moved
to the next bar or dropped.

Measure.add also refuses one outright, throwing MeasureCapacityException.

What does not exist

Nothing re-bars. Write five quarters into a 4/4 bar and you get five
quarters in one bar, drawn crammed together. There is no pass that takes the
overflow and carries it into the next measure.

Why this is a feature and not a bug fix

Re-barring restructures somebody's document, and every way of doing it makes a
musical decision that the caller may not want:

• Does the overflowing figure split? A half note starting on beat 4 of a 4/4
  bar cannot simply move — half of it belongs in this bar. The engraved answer
  is a quarter tied across the barline, which means synthesising a note that was
  never written and a tie that was never asked for.
• What happens to the bars after it? Pushing an overflow into bar 2 usually
  overflows bar 2, so the operation cascades to the end of the piece and every
  bar number after the first change moves.
• Which voice? Capacity is per voice. An overflow in voice 2 must not
  disturb voice 1's barlines.
• Is it even wrong? A cadenza, an unmetered passage and a deliberately
  over-full bar in contemporary notation are all real. Silently "fixing" them
  would be a worse defect than the silence this issue replaced.

So it must be something the caller asks for, not something an importer does
on its way past.

Proposed shape

A pure function over the model, not a mutation and not a parser behaviour:

/// Re-bars [staff] so no measure exceeds its meter, splitting and tying
/// figures that straddle a barline.
Staff rebar(Staff staff, {bool tieSplitNotes = true});

• Returns a new Staff; the input is untouched (ADR-005: layout and editing
  decisions are values).
• Reports what it did — how many bars were added, which notes were split — the
  same way the parsers report what they could not read.
• Available to the importers as an opt-in, never as a default.

Acceptance criteria

• Five quarters in a 4/4 bar become 4 + 1, with the fifth in a new measure.
• A half note straddling the barline becomes two quarters joined by a tie, and
  MidiMapper sounds it as ONE note of the original length.
• A pickup bar is left alone.
• An over-full voice 2 does not move voice 1's barlines.
• The result passes warnOverfullMeasures with no warnings.
• Round-trips: staffToMusicXML(rebar(s)) re-imports to the same music.

Requested by a user testing the Live Editor, who typed a fifth quarter into a
4/4 bar and reasonably expected either a refusal or the note to move on.