Test trigger exporting after timeout with partially filled queue

[Joannis]

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          @slashmo I'm struggling to test the scenario where the exporter triggers an export after a timeout - if the queue is not full yet

Originally posted by @Joannis in https://github.com/slashmo/swift-otel/issues/117#issuecomment-2381295209

This issue affects logging, but probably also affects metrics and/or tracing.