Add codspeed badge #178

Job	Run time
tests (ubuntu-latest, 3.11, highest)	1m 56s
tests (ubuntu-latest, 3.11, lowest-direct)	1m 47s
tests (ubuntu-latest, 3.12, highest)	1m 58s
tests (ubuntu-latest, 3.12, lowest-direct)	1m 57s
tests (ubuntu-latest, 3.13, highest)	4m 24s
tests (ubuntu-latest, 3.13, lowest-direct)	1m 59s
tests (macos-latest, 3.11, highest)	2m 37s
tests (macos-latest, 3.11, lowest-direct)	2m 17s
tests (macos-latest, 3.12, highest)	2m 6s
tests (macos-latest, 3.12, lowest-direct)	1m 54s
tests (macos-latest, 3.13, highest)	2m 6s
tests (macos-latest, 3.13, lowest-direct)	2m 38s
tests (windows-latest, 3.11, highest)	7m 9s
tests (windows-latest, 3.11, lowest-direct)	6m 19s
tests (windows-latest, 3.12, highest)	5m 26s
tests (windows-latest, 3.12, lowest-direct)	6m 6s
tests (windows-latest, 3.13, highest)	6m 49s
tests (windows-latest, 3.13, lowest-direct)	6m 50s
	1h 6m 18s

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