Add recordingSpan and currentSpan methods to TracerProtocol #21

Job	Run time
Cxx interop / Construct Cxx interop matrix	4s
Benchmarks / Construct Benchmarks matrix	2s
Unit tests / Construct unit test matrix	3s
Soundness / API breakage check	43s
Soundness / Documentation check	56s
Soundness / License headers check	3s
Soundness / Unacceptable language check	3s
Soundness / Broken symlinks check	7s
Soundness / Format check	30s
Soundness / Shell check	31s
Soundness / Python lint check	5s
Soundness / YAML lint check	3s
Benchmarks / Benchmarks / Linux (5.9)	2m 15s
Benchmarks / Benchmarks / Linux (5.10)	2m 8s
Benchmarks / Benchmarks / Linux (6.0)	2m 9s
Benchmarks / Benchmarks / Linux (nightly-6.0)	2m 35s
Benchmarks / Benchmarks / Linux (nightly-main)	2m 26s
Unit tests / Unit tests / Linux (5.9)	34s
Unit tests / Unit tests / Linux (5.10)	35s
Unit tests / Unit tests / Linux (6.0)	43s
Unit tests / Unit tests / Linux (nightly-6.0)	48s
Unit tests / Unit tests / Linux (nightly-main)	47s
Cxx interop / Cxx interop / Linux (5.9)	43s
Cxx interop / Cxx interop / Linux (5.10)	45s
Cxx interop / Cxx interop / Linux (6.0)	45s
Cxx interop / Cxx interop / Linux (nightly-6.0)	50s
Cxx interop / Cxx interop / Linux (nightly-main)	52s
	22m 5s

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