Keep sessions around between each ConanRequester #283

Job	Run time
Setup and Cache Dependencies	1m 32s
Conan (unittests) (3.8)	1m 15s
Conan (integration) (3.8)	3m 49s
Conan (functional) (3.8)	17m 24s
Conan (unittests) (3.12)	35s
Conan (integration) (3.12)	2m 44s
Conan (functional) (3.12)	16m 10s
Conan (unittests) (3.13)	37s
Conan (integration) (3.13)	1m 49s
Conan (functional) (3.13)	14m 58s
	1h 0m 53s

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