perf(event-bus): cache event propagation check

[xHeaven]

GenericEventBus checked whether the event class had #[StopsPropagation] inside the loop for every handler. So if one event had 50 handlers, it rebuilt reflection for the same unchanged event 50 times.

[github-actions]

Benchmark Results

Comparison of fix/event-bus-reflect-once against 3.x (c699ab834d421d13f092554fe749e3599d3ad026).

Open to see the benchmark results

Benchmark	Set	Mem. Peak	Time	Variability
QueryExecutionBench(benchExecuteInsert)	-	4.350mb +0.01%	10.129μs +7.49%	±1.18% -4.71%

_{Generated by phpbench against commit 83874b6}