Chore: Refactor infra/conf.TestToCidrList()

[zonescape]

Improvements:

• drop init() functions, use more straightforward code
• don't write geoip.dat into the project directory*
• don't write geoip.dat twice

*geoip.dat is written into the project directory if you have that file in ./resources only:

• init() function in dns_test.go sets environment variable xray.location.asset to os.Getwd() i.e. to infra/conf
• init() function in router_test.go writes geoip.dat to platform.GetAssetLocation() i.e. to infra/conf

[yuhan6665]

Thanks! Looks good to me