fix: better type safety for null checks and optional chaining

[ChefBingbong]

this PR improves null cheks around the code base to improve typesafety of code and to avoid optional chaining when accessing items or functions inside entities or objects, hence improving readabilit, code cleanliness and reliability.

changes

1. remove optional chaining and only access items inside objects if the entity is defined
2. improve the logic in the discv5 start and stop methods by reducing duplicate code and makinging sure ip4 or ip6 sokets are defined before attempting to open or close their connections

[CLAassistant]

All committers have signed the CLA.

[wemeetagain]

Hm, type-safety is a pretty objective measurement. I don't see any improvement from this PR. Reason being that optional chaining (a builtin language feature) has a quite clear meaning, and it is well modeled in TypeScript. Your change (1) is roughly (but not entirely!) equivalent, so it is mostly a lateral move wrt type-safety.

Wrt code cleanliness / readability / maintainability, this is somewhat subjective. And here I disagree with the changes you have. With 1, this is simply more verbose with no clear benefit. We think optional chaining is a useful syntax sugar and should be used in place of nullish checks in if or ternarys. We're firm on this. With 2, this is somewhat more subjective. But the intent in code here is to be explicit. We don't need to generically collect and iterate over sockets/configs, it doesn't even save us any lines of code! Because of the really limited/subjective benefit, I choose not to accept this change either.