Move threading.RLock to backports module
Reason:
pywikibot.threading.RLock was introduced with T151727 to implement compat's output cache. The only reason for this derived class was to have a locked() method which is used in terminal_interface_base.UI. With Python 3.14 this locked() method was implemented. The additional count property isn't used within the framework and can surely dropped if we went back to the standard Python implementation.
Steps
- move pywikibot.threading.RLock to backports module and implement it for Python < 3.13
- deprecate pywikibot.threading.RLock
- deprecate (or remove) count property