Improve string concat #193

Job	Run time
build (windows-latest, net7.0, x64)	4m 14s
build (windows-latest, net6.0, x64)	4m 10s
build (windows-latest, net5.0, x64)	2m 53s
build (windows-latest, netcoreapp3.1, x64)	4m 21s
build (ubuntu-latest, net7.0, x64)	59s
build (ubuntu-latest, net6.0, x64)	1m 7s
build (ubuntu-latest, net5.0, x64)	54s
build (ubuntu-latest, netcoreapp3.1, x64)	1m 15s
build (macos-13, net7.0, x64)	1m 24s
build (macos-13, net6.0, x64)	1m 16s
build (macos-13, net5.0, x64)	1m 22s
build (macos-13, netcoreapp3.1, x64)	1m 24s
build (windows-latest, net48, x64)	6m 17s
build (windows-latest, net48, x86)	3m 46s
build (windows-latest, net7.0, x86)	5m 8s
build (windows-latest, net6.0, x86)	4m 7s
build (windows-latest, net5.0, x86)	4m 7s
build (windows-latest, netcoreapp3.1, x86)	6m 16s
upload	1m 2s
	56m 2s

Provide feedback