Performance issue with CResourceHandler::makePackageResourceID

[shahchintan14]

The use of std::max_element in CResourceHandler::makePackageResourceID makes the time complexity of this method O(n) which results in making IDs for all resources in a package O(n2) i.e. quadratic.
This is a performance regression over older versions of lib3mf.

If there is a need to get the biggest ID, then it is better to make m_resourceIDs an (ordered) std::map instead of std::unoredered_map.
That way m_resourceIDs.rbegin()->first will give the biggest ID in constant time.

This will reduce the time complexity of CResourceHandler::makePackageResourceID to O(log(n)). There are other std::map look ups in that method, but log(n) is much better. Overall ID creation in entire package will be O(n * log(n)).

There will be a side effect of this change on 2 other methods of CResourceHandler - findResourceIDByUniqueID and removePackageResourceID. Their time complexities will increase from constant to O(log(n)). But overall performance of lib3mf should still be better.

This above fix could be implemented with minimal changes - replace unordered_map with map and max_element with rbegin()->first.
However, if the side effects are not acceptable, then it is best to maintain biggestID separately rather than finding it in linear fashion every time we make a new resource ID.

@martinweismann Any thoughts on this?

[shahchintan14]

Link to problem code:
https://github.com/3MFConsortium/lib3mf/blame/master/Source/Model/Classes/NMR_PackageResourceID.cpp#:~:text=UniqueIDPackageIdMap%3A%3Aconst_iterator%20biggestId,%7D)%3B

Instead of m_resourceIDs.rbegin() suggested above, we could use m_resourceIDs.crbegin().
m_resourceIDs.rend() can be used to check for empty map.

[shahchintan14]

@feliperoos Tagging you as I see your commit in this area of code.