fix: default sync timing to the wall clock (restore 2.1.0 multi-room sync)

[chrisuthe]

The regression

2.1.0 synchronized with other players correctly, no offset needed. 2.2.x is ~100ms out of sync. Bisecting the sync pipeline across the whole 2.1.0→2.2.x range (both repos) found a single change to when audio plays:

Release	Sync time source
v2.1.0	Wall clock — HighPrecisionTimer.Shared.GetCurrentTimeMicroseconds()
v2.2.x	WASAPI device clock — DeviceClockAnchor (commit d18dd27)

Nothing in the SDK 8.0.0→9.0.4 jump moved playback timing — external correction and the sync formula already existed in 8.0.0.

Why the device clock desyncs

The device clock reads the DAC-rendered position, which permanently lags the samples read from our buffer by the ~100ms WASAPI output prefill. So elapsed − samplesRead = −100ms forever — a constant error the corrector fights by inserting samples, shoving the player off the shared schedule. The wall clock advances 1:1 with real playback, so the startup prefill gulp self-corrects and steady-state error is ~0. No offset needed, exactly like 2.1.0.

It also bought us nothing: the DAC clock reports a 1.0000 ratio on the hardware tested (agrees with the system clock → zero drift benefit), and the #33 stutter was actually fixed by the concealment + output-driven feeding in #46 — not the clock.

Change

Default Audio:SyncCorrection:UseDeviceClock to false (wall clock) in appsettings.json, the config read, and the player constructor. The device clock stays available as an opt-in for genuinely divergent DAC clocks, with the existing automatic runtime wall-clock fallback intact.

Tests

New MultiRoomSyncAlignmentTests drives the real TimedAudioBuffer + SyncCorrectionCalculator + SyncCorrectedSampleSource through a drift-free session and asserts:

• no startup offset → player holds the server schedule (sync error ~0, in sync);
• an uncompensated prefill (the device-clock failure mode) → player drifts ~100ms off schedule.

Full suite green (97/97).

Verify

Merging publishes a dev build. The decisive check: this player back in sync with other Sendspin players with StaticDelay at 0, as in 2.1.0.

Refs #33.