Extends the #163 PlayoutBuildGoldenTests in-memory net to the Sequential (YAML)
builder: a committed fixture (Goldens/Fixtures/sequential-schedule.yml) with two
`count: 2` instructions over one chronological collection, built via
SequentialPlayoutBuilder over the pinned window. The count/all/duration handlers
do UTC-only arithmetic off the caller-supplied start, so the case is
TZ-independent (passes, not skips, under a non-UTC TZ) and needs no Assume guard.
Non-vacuity: a fixture count tweak flips the golden + the contiguity assertion.
Scripted is deliberately excluded from the golden net — ScriptedPlayoutBuilder
shells out via Cli.Wrap to an external process that drives SchedulingEngine over
HTTP, which no in-memory golden can characterize. Recorded as the Done-when
"documented decision" arm in docs/decisions.md
(testing.scripted-playout-golden-deferred) + docs/testing.md; the scripted
integration harness is tracked as follow-up #563.
fixes#381
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>