Optimize CCustomData

[Pirulax]

Changelog:

• Removed redundant m_SyncedData
• Changed map type to CFastHashMap as we want the absolute maximum performance
• Removed IterBegin and IterSyncedBegin. Replaced it with GetAll() for based range loop
• Changed const char* for the name (in function argument list) to const std::string& because when searching in the hash map we'll need to use std::string anyways (Thats how it works sadly)
• I'll open a separate PR for more changes, because this can be optimized even further

Note:

• This is only the server side. I'll open a separate PR - because I dont want to spam this one with changes, would make it hard to review - which will move all this to Shared