Split go sources into packages

[Ayake-QAware]

Due to simplicity, currently everything is in the main package. When the complexity of the code gets larger it may make sense, to split the go source into multiple packages and sub-directories. In that case, we also need to take care of the capitalization, since only objects starting uppercase will be publically visible: https://go.dev/doc/effective_go

[Ayake-QAware]

At the current moment, the complexity is limited and a restructuring is not necessary.

[GollyTicker]

This'll remain low complexity for a long while, so we'll not fix this.