The suite had accumulated breakage from prior refactors:
- selection unification: rewrite the integration tests for the single
unified clip_instances collection (shapes+clips are one set now).
- tempo-map: thread a TempoMap (constant 60 BPM = identity) into the
clip remap_time tests so the second-based expectations hold.
- drop two dead rgba_to_yuv420p tests that asserted tight plane sizes
incompatible with the function's 16-macroblock alignment.
- ignore the WIP theme var() cascade test (theme system not wired up).
Also a real bug the tests caught: auto_key_ranges produced overlapping
sample key ranges (the midpoint key mapped to both adjacent samples).
Start each range one past the previous midpoint.
da65b63bdf