Fix AggregateException

[pawelprazak]

• preserve cause and all other causes

Example:

val errors = NonEmptyVector(
      DecodingError("error1", label = Label.fromNameAndType("dummy1", "dummy:pkg:Dummy1"), cause = Exception("cause1")),
      DecodingError("error2", label = Label.fromNameAndType("dummy2", "dummy:pkg:Dummy1")),
      DecodingError("error3", label = Label.fromNameAndType("dummy3", "dummy:pkg:Dummy1"))
    )
    val aggregated = AggregatedDecodingError(errors)

besom.internal.AggregatedDecodingError: Decoding Errors [3]:
  error1
  error2
  error3
(with aggregate stack trace)
	at besom.internal.AggregatedDecodingError$.apply(codecs.scala:100)
	at besom.internal.InternalTest.$init$$$anonfun$34(EncoderTest.scala:996)
	at munit.internal.console.StackTraces$.dropOutside(StackTraces.scala:12)
	...
	at munit.internal.junitinterface.JUnitTask.execute(JUnitTask.java:87)
	at scala.build.testrunner.TestRunner$.runTasks(TestRunner.scala:70)
	at scala.build.testrunner.DynamicTestRunner$.main(DynamicTestRunner.scala:260)
	at scala.build.testrunner.DynamicTestRunner.main(DynamicTestRunner.scala)
Caused by: besom.internal.DecodingError: [dummy1[dummy:pkg:Dummy1]] error1
	at besom.internal.DecodingError$.apply(codecs.scala:80)
	at besom.internal.InternalTest.$init$$$anonfun$34(EncoderTest.scala:992)
	... 53 more
	Suppressed: besom.internal.DecodingError: [dummy2[dummy:pkg:Dummy1]] error2
		at besom.internal.DecodingError$.apply(codecs.scala:81)
		at besom.internal.InternalTest.$init$$$anonfun$34(EncoderTest.scala:993)
		... 53 more
	Suppressed: besom.internal.DecodingError: [dummy3[dummy:pkg:Dummy1]] error3
		at besom.internal.DecodingError$.apply(codecs.scala:81)
		at besom.internal.InternalTest.$init$$$anonfun$34(EncoderTest.scala:994)
		... 53 more
Caused by: java.lang.Exception: cause1
	... 54 more