Don't use namespaces

[pranitbauva1997]

When we are dealing with various outside libraries, we should always avoid using using namespace ....

It is not important right now, but when we would be using gRPC or something other, they might have few functions clashing.

PS: there are two implementations of pthread, one by Google and the other is the standard one. Since we are not using threads right now, it is okay. But we do plan to use them in future so fix this.