Small

chore: code cleanup for `associative_vector` #116

Job	Run time
Windows-MSVC/2019/Static/X86/Release	3m 3s
Windows-MSVC/2019/Static/X64/Release	2m 29s
Ubuntu/20.04/Static/X64/Release	1m 8s
MacOSX/10.15/Static/X64/Release	1s
	6m 41s

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