Add support for GTFS route colors #538

Job	Run time
formatting	51s
macos (macos-x86_64, On)	10m 11s
linux (linux-amd64-release, linux-amd64)	5m 56s
msvc (Debug)	1m 3s
macos (macos-arm64)	10m 1s
linux (linux-x86-release, linux-x86)	6m 3s
msvc (Release)	30s
linux (linux-arm-release, linux-arm, qemu-arm-static)	6m 8s
linux (linux-arm64-release, linux-arm64, qemu-aarch64-static)	6m 10s
linux (clang-tidy)	4m 11s
linux (linux-sanitizer)	1m 57s
linux (linux-debug, valgrind --leak-check=full --error-exitcode=1)	2m 27s
	55m 28s

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