docs: cleanup/rewrite

[bghira]

This pull request updates both the README.md and BENCHMARKS.md files to provide clearer, more concise, and better-structured documentation for users and contributors. The changes focus on improving usability by clarifying installation steps, usage examples, API descriptions, implementation details, and benchmark instructions, while removing outdated or redundant information.

Documentation and usability improvements:

• Major rewrite of README.md to provide a concise project overview, clearer install instructions for both Python and Rust, and practical usage examples for each language. The new format uses tables for API and implementation details, and removes redundant or outdated sections.
• Updated the Python API documentation to use tables for function signatures, input/output types, and constraints, making it easier to find and understand available functions and their requirements.
• Added a Rust usage example with a minimal, idiomatic code snippet, and clarified the feature set and build requirements for both Python and Rust users.
• Simplified and reorganized the BENCHMARKS.md file to focus on how to run benchmarks, what is measured, and how to interpret results. Removed point-in-time timing tables and replaced them with instructions for saving and annotating results, as well as tables describing measured operations and comparison constraints.
• Added sections to both files that clarify limitations, input requirements, and the non-drop-in nature of the Python API compared to OpenCV, helping set correct expectations for new users. [1] [2]