Need independent HighsLpRelaxation instances and mipdata_ = decltype(… #3841

Job	Run time
debug_all_tests (ubuntu-latest)	3m 53s
debug (ubuntu-latest)	3m 37s
debug64 (ubuntu-latest)	3m 54s
debug64_all_tests (ubuntu-latest)	3m 56s
release (ubuntu-latest)	3m 35s
release_all_tests (ubuntu-latest)	3m 31s
Release64 (ubuntu-latest)	3m 45s
Release64_all_tests (ubuntu-latest)	3m 37s
	29m 48s

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