chore: avoid microtasks when flushing sync (alternative)

[Rich-Harris]

Alternative to #15855 with same-or-better performance (the differences on the benchmark comparison are just noise)

sbench_create_signals
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 439.97ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 441.55ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 197.34ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 194.39ms
sbench_create_0to1
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.87ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.82ms
sbench_create_1to1
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 21.87ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 21.84ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.77ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.74ms
sbench_create_2to1
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 19.89ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 19.46ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.80ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  2.70ms
sbench_create_4to1
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 18.13ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 18.54ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.77ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  2.68ms
sbench_create_1000to1
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 16.78ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 16.61ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.76ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.78ms
sbench_create_1to2
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 10.65ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 10.75ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.60ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.68ms
sbench_create_1to4
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 8.57ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  8.16ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.49ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.52ms
sbench_create_1to8
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 6.75ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  6.31ms
sbench_create_1to1000
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   4.62ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 5.13ms
kairo_avoidable_owned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 297.36ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 295.26ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 7.46ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 7.38ms
kairo_avoidable_unowned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 400.70ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 399.96ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 6.61ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 6.66ms
kairo_broad_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 431.46ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 434.64ms
kairo_broad_unowned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  431.08ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 444.73ms
kairo_deep_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 189.08ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 193.74ms
kairo_deep_unowned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 928.16ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 924.90ms
kairo_diamond_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 286.58ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 288.65ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.36ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  4.22ms
kairo_diamond_unowned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 393.78ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 397.18ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.58ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.53ms
kairo_triangle_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 94.42ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 94.50ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.66ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.60ms
kairo_triangle_unowned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 215.03ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 215.11ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.71ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.73ms
kairo_mux_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 316.02ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 317.30ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   2.04ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.28ms
kairo_mux_unowned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 475.75ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 475.16ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   2.26ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.45ms
kairo_repeated_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 45.46ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 46.23ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.22ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.22ms
kairo_repeated_unowned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 46.42ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 47.09ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.22ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.20ms
kairo_unstable_owned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 77.92ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 79.54ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.82ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.74ms
kairo_unstable_unowned
  time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 96.12ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 97.83ms
  gc_time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.93ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.90ms
mol_bench_owned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 280.24ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 279.20ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.30ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.33ms
mol_bench_unowned
  time: fastest is b (flush-sync-2)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 297.42ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 296.95ms
  gc_time: fastest is a (flush-sync)
    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.26ms
    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.26ms

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