[rcasia]

Summary

Decomposes model/junit_result.lua (the largest file in the codebase)
by responsibility. Two rounds:

Round 1 — split pure JUnit-XML parsing concerns out of the class:

• model/junit_failure.lua: failure/error XML node parsing + stack-trace
  line-number scraping
• model/junit_status.lua: pass/fail/skip status derivation

Round 2 (based on review feedback) — separated the remaining
file-writing responsibility out of the class entirely:

• JunitResult had a private create_file_with_content doing real I/O
  (nio.fn.tempname, io.open, write, close), called directly from
  :result()/merge_results(). This tangled 'what happened in this
  test' (domain logic) with 'persist this output for neotest to read' (an
  I/O concern) in the same class.
• New util/output_writer.lua: the only module that knows about
  io.open/nio.fn.tempname now. Function-as-constructor DI,
  fully unit-testable without touching disk.
• model/junit_result.lua is now pure — no nio/io requires at all.
  :result()/.merge_results()/SKIPPED/ERROR return plain data
  (status/output_lines/errors/short) instead of a
  neotest.Result with an already-written file path.
• core/result_builder.lua composes the final neotest.Result via a new
  to_neotest_result(data, output_writer), since it already owned
  tempname_fn in its deps — the natural place for this conversion.
• Added tests/unit/test_output_writer_spec.lua (new module) and
  tests/unit/test_junit_result_spec.lua (JunitResult had no dedicated
  spec file before this refactor — closed that gap).

Result

• model/junit_result.lua: 324 -> 229 lines, zero I/O
• New: model/junit_failure.lua (81), model/junit_status.lua (37),
  util/output_writer.lua (69)
• Public API of JunitResult changed: :result()/.merge_results()/
  SKIPPED/ERROR now return plain data, not a neotest.Result with a
  file path — callers (only result_builder.lua) must pass it through
  output_writer.write(...).
• 203 test cases, 0 fails. luacheck: 0 warnings across 83 files.

Todo

• Establish baseline: run full test suite, note pass count, read junit_result.lua fully + its consumers + its existing tests
• Extract failure/error-node parsing + stack-trace scraping into a focused helper
• Extract status-derivation logic into a focused helper
• Reduce duplication between result() and merge_results() by sharing primitives
• Add focused unit tests for newly extracted modules
• Run make test, stylua --check, luacheck — all green, same or higher pass count
• Mark PR ready for review

Follow-up: separate file-writing from JunitResult (per review feedback)

• Extract a new util/output_writer.lua owning all io.open/nio.fn.tempname calls
• Make model/junit_result.lua pure (no I/O): result()/merge_results()/SKIPPED/ERROR return plain data
• core/result_builder.lua composes the final neotest.Result via output_writer
• core/junit_result_reader.lua no longer threads tempname_fn through to JunitResult
• Add tests/unit/test_output_writer_spec.lua and tests/unit/test_junit_result_spec.lua (new — no dedicated spec existed before)
• Update existing tests referencing the removed tempname threading
• Full suite green (203 cases, 0 fails), luacheck clean (83 files)