feat: Improved custom tracing span API #17

Job	Run time
Build and publish artifacts and plugins locally	2m 37s
Basic checks	57s
Check service docker image contents	41s
Run annotation processor tests	1m 41s
Run sbt test	4m 2s
Maven samples (shopping-cart-quickstart, true)	45s
Maven samples (choreography-saga-quickstart, true)	55s
Maven samples (doc-snippets, false)	32s
Maven samples (view-store, true)	1m 13s
Maven samples (spring-dependency-injection, true)	47s
Maven samples (event-sourced-customer-registry, true)	1m 13s
Maven samples (event-sourced-counter-brokers, docker compose up -d, true)	1m 29s
Maven samples (event-sourced-customer-registry-subscriber, true, ./start-upstream.sh)	1m 5s
Maven samples (key-value-counter, true)	47s
Maven samples (key-value-shopping-cart, true)	41s
Maven samples (key-value-customer-registry, true)	59s
Maven samples (tracing, false)	27s
Maven samples (reliable-timers, true)	43s
Maven samples (transfer-workflow, true)	40s
Maven samples (transfer-workflow-compensation, true)	1m 4s
	23m 18s

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