Enable subclassing of RoutingCost from python #234

Job	Run time
formatting	7m 2s
lint	29m 3s
test (noetic)	17m 41s
test (galactic)	14m 16s
test (humble)	8m 36s
full_conan_installation (3.8)	13m 29s
full_conan_installation (3.9)	13m 21s
full_conan_installation (3.10)	12m 55s
full_conan_installation (3.11)	12m 54s
full_conan_installation (3.12, manylinux_2_31_x86_64, conanio/gcc10:latest)	13m 9s
	2h 22m 26s

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