fix: DirectionWriter respects orderedComponents

[webern]

Summary

• Split DirectionWriter::getDirectionLikeThings() into two emission paths:
  fixed-order (existing behavior when orderedComponents is empty) and ordered
  dispatch (uses the component order the reader recorded from parsed XML).
• Extract each per-kind emission block into a private helper method on
  DirectionWriter, called by both paths to avoid ~400 lines of duplication.
• Ordered dispatch loops over orderedComponents, bounds-checks each index, and
  calls the appropriate helper. Words are bundled on first encounter; chords are
  skipped (emitted via createHarmonyElements).
• Add doc comment on DirectionData::orderedComponents explaining its
  round-trip role and the "do not populate programmatically" contract.

Corpus impact

Discovery mode (94 PASS / 737 FAIL) shows no new files unlocked by this fix
alone. Files with interleaved direction-types (e.g. ly31a_Directions.xml,
ly31c_MetronomeMarks.xml) still fail due to other blockers:

• ly31a_Directions.xml: child count mismatch at .../note (unrelated to
  direction ordering)
• ly31c_MetronomeMarks.xml: attribute count mismatch at
  .../direction-type/metronome (missing metronome attributes, not ordering)

This fix is a prerequisite for those files to eventually pass — the ordering
divergence was one of multiple blockers, not the sole blocker. A synthetic
round-trip test that isolates the ordering behavior would strengthen coverage
here.

Fixes #206

[github-actions]

Coverage report

Core-dev coverage src/private/mx/core/

Metric	Coverage	Covered / Total
Lines	77.8%	28487 / 36624
Functions	74.3%	6349 / 8550
Branches	50.6%	22632 / 44725

API coverage src/private/mx/{api,impl,utility}/

Metric	Coverage	Covered / Total
Lines	78.5%	6003 / 7647
Functions	63.6%	2022 / 3177
Branches	47.7%	5082 / 10665

Core HTML report | API HTML report

Commit e73aa71ee444c48062e2a72bbe782e4a7e7b991a.

[github-actions]

gen-quality gen/

gen-quality: 84.5 / 100   (floor 84.5, +0.0)

  structure     86.5  x0.50   [fn 90.5 / file 82.6]
  cyclomatic    88.4  x0.25
  cognitive     76.6  x0.25

  409 functions across 31 files, 7702 lines (largest file 1044)
  max cc 56  max cognitive 44  max fn loc 152

Worst offenders (top 5 per axis; full lists in score.json):
  cyclomatic gen/xsd/analyze.py:311     report                             56
  cyclomatic gen/plates/build.py:956    _validate_config_against_ir        35
  cyclomatic gen/press/context.py:145   plate_context                      34
  cyclomatic gen/__main__.py:46         _ir                                23
  cyclomatic gen/tests/test_ir.py:102   _check_references                  20
  cognitive  gen/xsd/analyze.py:311     report                             44
  cognitive  gen/ir/resolve.py:119      flat_elements                      40
  cognitive  gen/tests/test_ir.py:102   _check_references                  38
  cognitive  gen/press/context.py:145   plate_context                      37
  cognitive  gen/xsd/analyze.py:207     _sccs                              37
  size       gen/xsd/analyze.py:311     report                             152
  size       gen/press/context.py:145   plate_context                      96
  size       gen/plates/build.py:533    _value_plate                       89
  size       gen/plates/build.py:956    _validate_config_against_ir        89
  size       gen/ir/resolve.py:119      flat_elements                      78

Commit e73aa71ee444c48062e2a72bbe782e4a7e7b991a.