Only AddNode() had some valid use cases for AddNodeOption, but yet
the params were propagated everywhere.

As I surprised myself it works even with 0 or 1 nodes.

Added no useful functionality as it was just combining 2 simple
methods and the function was only used in its own test.

The method was used only its own test.

As the concept and the related functionality was not used anywhere.

As the concept and the related functionality was not used anywhere.

That also makes AddNodeOption type and the AddNode's AddNodeOptions
parameter unnecessary.

As we can just call Stop() on Network.

The utility of this function was very low. The method just combined
two simple calls into one and was used in only one place.

Note: verifyRing() now can be private.

This was the lat mixed responsibility function in node.go, i.e.,
not just adding but connecting nodes. As the responsibility of
connecting nodes belongs to p2p/simulations/connect.go I removed the
method.

Note: there was just one complex use case for AddNodesAndConnectChain
in testSwarmNetwork where we actually added nodes more than once and
we still wanted to keep them in chain topology. There I introduced
a test helper function.

The deleted methods were all unused. So I don't want to maintain them
during refactor.

- typos
- unused global variable
- unused function parameters
- redundant import alias
- code style issue: snake case

- typos
- redundant import alias

During my code cleanup efforts I removed the AddNodeOption type and
related functionality. As that was not used anywhere.

However, during code review I was asked to bring back the functionality.
Here I'm doing that; still, I would prefer to follow YAGNI.