Document oslib - #47

PR Description:

This PR enhances the oslib.h header file by adding comprehensive Doxygen-style documentation. The updates include:

• File Overview: Added a brief introduction to the file's purpose within OSLib.
• Module Descriptions: Grouped related functions and variables under clear sections (general, sync, memory, maths, debug, misc).
• Detailed Documentation:
  • Documented key variables, function pointers, and functions.
  • Added explanations for macros, particularly those related to memory management and benchmarking.
  • Clarified platform-specific differences between PSP and non-PSP environments.

Impact:

• No functional changes.
• Improved readability: The documentation provides clear guidance for developers, making the library easier to use and maintain.

This PR prepares the codebase for better developer onboarding and automated documentation generation.