Chunk iterator and fix getter

[nhatdongdang]

This pull request introduces the following enhancements to the Chunk class:

1. Addition of Iterator class:

   • Implemented an Iterator class within Chunk to enable traversal of the 3D block data using standard iterator patterns.
   • Added the begin() and end() methods to support range-based loops and iterator-based algorithms.

2. Doxygen-style documentation:

   • Documented the Iterator class, including all its methods (operator*, operator->, operator++ (prefix and postfix), operator==, operator!=), as well as the begin() and end() methods.
   • Provided clear descriptions of the iterator's functionality and the purpose of each method.

3. Test Cases:

   • Tests include verifying iteration over the Chunk data.

4. Fix getter:

   • Fix chunk getter method.