fix(producer): tolerate rounded frame-boundary durations

[miguel-heygen]

What

• avoid an extra output frame when a decimal duration is a serialized approximation of an exact frame boundary
• retain ceiling behavior for durations that genuinely extend into the next frame

Why

At 30fps, a static duration of 32.866667 represents 986 frames after six-decimal serialization. Multiplication yields 986.00001, so the producer probe stage's raw Math.ceil scheduled 987 frames and required a post-render one-frame trim.

How

Convert duration to frame count by snapping values within 0.001 frame of an integer boundary, otherwise ceiling as before. This tolerance is wider than six-decimal metadata error even at high frame rates, while remaining far below a visible frame interval.

Test plan

• added a regression test that first failed with 987 and now returns 986 for 32.866667 at 30fps
• added a guard test confirming 32.867 still ceilings to 987
• bun test packages/producer/src/services/render/stages/probeStage.test.ts
• bun run --filter @hyperframes/producer typecheck
• bunx oxlint packages/producer/src/services/render/stages/probeStage.ts packages/producer/src/services/render/stages/probeStage.test.ts
• pre-commit lint, format, fallow, and typecheck hooks passed