Refactor build.zig for Enhanced Readability and Dynamic Test Inclusion

[hendriknielaender]

#22

Enhanced Readability and Maintainability:

• The script has been modularized into distinct functions: setupLibrary, setupTesting, setupExamples, and setupDocumentation. This modularization separates concerns, making the script more readable and easier to maintain.
• Each function is responsible for a specific aspect of the build process, thereby reducing complexity and improving the overall structure of the script.
• Comments and documentation within the script have been added or updated to reflect these changes, providing clear guidance on the purpose and functionality of each part of the script.

Dynamic Inclusion of Test Files:

• A significant enhancement in the setupTesting function is the dynamic discovery and inclusion of .zig test files from specified directories.
• This is achieved by iterating over the contents of each directory listed in the test_dirs array, automatically adding any .zig files found as test cases.
• This approach removes the need for manually listing test files, allowing for easier management of tests, especially in larger projects with numerous test cases spread across multiple directories.