api: segno and coda suport

[webern]

Summary

mx::api exposed SegnoData/CodaData but support was partial: the reader only captured position
and color (and even then never set isColorSpecified, so color was dropped), and the writer emitted
nothing for segno or coda, silently losing them on write.

This widens both data classes to the full <segno>/<coda> attribute surface and makes the trip
lossless in both directions:

• Added fontData, smufl (+ isSmuflSpecified), and id (+ isIdSpecified) to SegnoData and
  CodaData. Position and halign/valign already ride along in positionData.
• DirectionReader::parseSegno/parseCoda now read font, smufl, id, and set isColorSpecified.
• DirectionWriter now writes segno and coda (position, font, color, smufl, id), replacing the
  lossy MX_UNUSED stub proposed in the superseded PR.

Note: positionData carries a placement member that does not apply to <segno>/<coda>
(placement lives on the parent <direction>). The read/write helpers are attribute-tolerant
(if constexpr (requires ...)), so this is inert, not a data bug. Documented in the headers.

Testing

• New impl round-trip test segnoAndCodaRoundTrip_DirectionWriter: builds a segno and a coda
  with every field set, writes via DirectionWriter, reads back via DirectionReader, asserts
  equality. Passes (8 assertions in 2 test cases with the existing ottava test).
• make dev builds clean; make fmt applied.
• Full make test deferred to CI.

TODO (planned, not done in this PR)

• api: add api-level round-trip test for segno/coda synthetic fixtures #204 Add an api-level round-trip test over data/synthetic/segno.{3.0,3.1}.xml and
  coda.{3.0,3.1}.xml (register them in MxFileRepository) so the public DocumentManager path is
  exercised, not just the impl layer. These fixtures already carry every attribute (the 3.1 variants
  add id and smufl).
• impl: implement rehearsal writing in DirectionWriter #205 Implement rehearsal writing in DirectionWriter. Rehearsals are read but not written; PR Add support for segno reading #134
  bundled a lossy rehearsal writer. Scoped out here to keep this segno/coda-only.
• impl: DirectionWriter ignores orderedComponents — interleaved direction-type children lose original order on write #206 Honor orderedComponents in DirectionWriter. The writer emits each component kind in its own
  loop (segnos, then codas), so direction-type children interleaved with other kinds are not
  guaranteed to round-trip in original order. Pre-existing limitation surfaced by this work.
• impl: parseWords never sets WordsData.isColorSpecified — words color does not round-trip #207 Fix the same latent bug in parseWords: WordsData.isColorSpecified is never set on read, so
  words color does not round-trip (same bug class fixed here for segno/coda).

References

• Closes Implement segno reading #133
• Supersedes Add support for segno reading #134

[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 711beff9b90591806b14f870563027242bf34185.

[github-actions]

Coverage report

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

Metric	Coverage	Covered / Total
Lines	77.9%	28539 / 36620
Functions	74.4%	6360 / 8548
Branches	50.7%	22672 / 44725

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

Metric	Coverage	Covered / Total
Lines	71.4%	5181 / 7260
Functions	59.9%	1815 / 3029
Branches	42.5%	4322 / 10169

Core HTML report | API HTML report

Commit 711beff9b90591806b14f870563027242bf34185.