Bmi_Adapter cleanup, de-template #1637

Job	Run time
test_mpi_remote_nexus (ubuntu-latest)	2m 12s
test_bmi_c (ubuntu-latest)	3m 33s
test_pet (ubuntu-latest)	3m 21s
test_bmi_c (macos-latest)	10m 22s
test_unit (ubuntu-latest)	5m 10s
test_pet (macos-latest)	4m 54s
test_unit (macos-latest)	8m 57s
test_bmi_cpp (ubuntu-latest)	3m 45s
test_bmi_fortran (ubuntu-latest)	3m 44s
test_bmi_cpp (macos-latest)	7m 11s
test_bmi_fortran (macos-latest)	6m 1s
test_bmi_multi (ubuntu-latest)	4m 26s
test_bmi_python (ubuntu-latest)	4m 24s
test_bmi_multi (macos-latest)	10m 23s
test_bmi_python (macos-latest)	6m 23s
	1h 24m 46s

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