refactor: move source code to src directory

[ctran88]

What's New?

• moves source code from custom/lib/ to src/ to conform with modern php lib practices
• moves tests out of source directory and into a root tests/ directory

Screenshots (if appropriate):

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have manually tested my code thoroughly
• I have added/updated inline documentation for public facing interfaces if relevant
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing integration and unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Additional context

[vanessa-passage]

Code changes look good.

Curious if nesting this under /custom was creating problems or was this just to streamline the file structure?

[ctran88]

Code changes look good.

Curious if nesting this under /custom was creating problems or was this just to streamline the file structure?

it was just to streamline it based on looking around at various php libs