Adds 5 tests to StreamingRegionTwoTierTests covering all tier-transition paths:
- FarToNear promote (walk 2 east from initial center)
- NullToNear teleport (loads 9 near + 40 far for a fully fresh region)
- NearToFar demote only after NearRadius+2 hysteresis threshold
- FarToNull unload only after FarRadius+2 hysteresis threshold
- oscillation no-thrash: bouncing 1 LB across a near boundary fires 0 demotes
and at most 5 promotes total (one initial settle of the x=100 near-column)
Oscillation test fix: initialise the region at the oscillation midpoint
(103,100) rather than at a distant starting center (100,100) so the
initial move into the oscillation range doesn't itself trigger legitimate
demotes, isolating the no-thrash invariant.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
326b698161