refactor split_str_once #7485

Job	Run time
Windows (Release, MSVC, x64)	23m 38s
Windows (FastDebug, MSVC, Win32)	22m 40s
Windows (Release, MSVC, Win32)	21m 26s
Mac (Debug, clang, x86_64)	6m 55s
Windows (Debug, MSVC, x64)	14m 8s
Mac (Release, clang, arm64)	8m 54s
Mac (Debug, clang, arm64)	7m 51s
Windows (Debug, MSVC, Win32)	14m 40s
Mac (Release, clang, x86_64)	6m 39s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=ON)	15m 5s
Linux (Debug, clang-16)	16m 44s
Linux (Release, clang-16)	20m 48s
Linux (Debug, gcc-9)	18m 22s
Windows (FastDebug, MSVC, x64)	25m 42s
Linux (Debug, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	14m 35s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=ON)	19m 4s
Linux (Release, gcc-13)	16m 45s
Linux (Release, gcc-13, -DFSO_BUILD_WITH_OPENGL=OFF -DFSO_BUILD_WITH_VULKAN=OFF)	17m 44s
Linux (Debug, gcc-13)	14m 38s
Linux (Release, gcc-9)	19m 48s
	5h 26m 6s

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