Brief summary of issue / Description of requested feature:

Using unsigned type is an anti-pattern according to modern C++ guidelines:
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-nonnegative

We should avoid it in the future and remove its use in existing code.

Steps to reproduce the issue / Reasons for adding feature:

1. Review src/dlgRoomSymbol.cpp
2. Function has a signature like: void dlgRoomSymbol::init(QHash<QString, unsigned int>& pSymbols, QSet<TRoom*>& pRooms)

Error output / Expected result of feature

2. Function nowadays is signed by using standard int alright
3. But that particular case was not the only one. A search for "unsigned" finds 100+ places in almost 50 different files.

Extra information, such as the Mudlet version, operating system and ideas for how to solve / implement:

Originally noted / requested by Vadi here: #4573 (comment)

See also Expects: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#i6-prefer-expects-for-expressing-preconditions