fix: clean and normalize module imports

[LNSD]

From discord (@arnetheduck):

hm, looks like some waku imports are a bit off - take for example https://github.com/waku-org/nwaku/blob/master/waku/v2/node/peer_manager/peer_manager.nim#L15 - the ../.. works because of an unfortunate quirk in Nim when compiling a top-level project in a suitable folder, but the file is actually not available in that location - instead, it actually resides in ../../../../waku/v2/protocol/waku_relay (or simply ../protocol/waku_relay) preventing the use of the module from "outside", ie when importing waku in a stand-alone application - I think this might be the leftover of some refactoring? cc @LNSD

This PR aims to fix this issue.

[jakubgs]

Thanks! I tested this with our Nix derivation from:

• nwaku: init at 0.16.0 NixOS/nixpkgs#193679

And it works:

 > nix-build -A nim-waku .
/nix/store/z6x53di4xpk9j2lx0z2m75iznfjsyb57-nwaku-fb506e9196e2838b2dad08de011f120c62f46e90-fb506e91

 > $(nix-build -A nim-waku .)/bin/wakunode2 --version                                                                           
version / git commit hash: fb506e9196e2838b2dad08de011f120c62f46e90

[jm-clius]

LGTM, assuming it fixes the issue. (Sounds like it does.)