Selector block: fix sign-conversion warnings & minor cleanup #2102

Job	Run time
Update the docker container if it is modified	9s
clang-18, \| Release	2h 4m 2s
clang-18, \| Debug	2h 47m 18s
emcc \| Debug	1h 42m 10s
emcc \| Release	1h 53m 34s
gcc-13 \| Debug	59m 56s
gcc-13 \| Release	2h 6m 43s
gcc-14 \| Debug	2h 44m 35s
gcc-14 \| Release	4h 48m 53s
	19h 7m 20s

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