make environment config protected members, resolves #285 #328

Job	Run time
check-single-include	5s
test-ubuntu-20.04-gcc-9	1m 4s
test-ubuntu-20.04-gcc-11	1m 15s
test-ubuntu-20.04-clang-9	1m 22s
test-ubuntu-20.04-clang-12	1m 14s
test-ubuntu-22.04-clang-15-no-exceptions	50s
test-ubuntu-22.04-gcc	49s
test-ubuntu-24.04-gcc	56s
test-windows-2019-msvc	1m 13s
test-windows-2019-clang	2m 0s
test-windows-2019-gcc	2m 0s
test-windows-2022-msvc	1m 27s
test-macOS-12-gcc	1m 55s
test-macOS-13-clang	2m 56s
	19m 6s

Provide feedback