text: Title: Libdoc performance degradation starting from RF 6.0
  Body: In the project I'm working on we use dynamic python libraries with 10k+ keywords. After migrating to RF 6.0 we noticed that the libdoc execution time doubled. 
  
  Here is a comparison of the time taken by libdoc in each version given the same parameters:
  
  ![image](https://github.com/user-attachments/assets/bc0da080-730f-4629-9c86-911282bc9420)
  
  Digging into the code a bit I noticed that there is a class called `Languages` that is instantiated once for each Keyword, but could be instanciated once and use n times. Here is a pyinstrument screenshot:
  
  ![image](https://github.com/user-attachments/assets/afde0b98-6077-429e-aa47-9fcc726080c8)
  
  ## Proposed Fixes
  
  * Suggestion 1: A pre-created instance of `Languages` could be provided when calling `TypeConverter.converter_for`:
  https://github.com/robotframework/robotframework/blob/c9c9d414d8aa66959d3df7ef1895516c1d37d6c2/src/robot/libdocpkg/datatypes.py#L55
  
  * Suggestion 2: Convert the class `Languages` into a singleton.
  