test

Add the 'btree' benchmark. #1821

Job	Run time
ubuntu-latest - 3.9	6m 20s
ubuntu-latest - 3.10	6m 38s
ubuntu-latest - 3.11	7m 30s
ubuntu-latest - 3.12	7m 59s
ubuntu-latest - 3.13	8m 1s
ubuntu-24.04-arm - 3.9	5m 41s
ubuntu-24.04-arm - 3.10	5m 55s
ubuntu-24.04-arm - 3.11	6m 34s
ubuntu-24.04-arm - 3.12	7m 13s
ubuntu-24.04-arm - 3.13	6m 45s
ubuntu-latest - 3.13 free-threading	7m 58s
ubuntu-24.04-arm - 3.13 free-threading	6m 47s
ubuntu-latest - 3.14-dev	7m 36s
ubuntu-latest - 3.14-dev free-threading	7m 53s
ubuntu-latest - pypy-3.10	10m 41s
ubuntu-latest - pypy-3.9	10m 10s
macos-latest - 3.13	6m 41s
windows-latest - 3.13	12m 57s
	2h 19m 19s

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