refactor: drop helper functions

[Greg0]

Summary

This PR replaces global helper functions with static constructors on their respective classes, providing better developer experience through IDE autocompletion, improved code organization, and more efficient autoloading. It will give similar experience to Java SDK.

Changes

1. Replace createInstance function with static constructor

• Moved the createInstance() global function to a static method on the Featurevisor class
• All instantiation is now done through Featurevisor::createInstance()
• Improves IDE completion and static analysis

2. Replace createLogger function with static constructor

• Moved the createLogger() global function to a static method on the Logger class
• All logger instantiation is now done through Logger::create()
• Removed unnecessary functions.php file as all helpers have been moved to their classes

Migration Impact

This is a backward-incompatible change that requires users to update their code to use the static constructors:

• Replace use function Featurevisor\createInstance; with use Featurevisor\Featurevisor;
• Replace createInstance([...]) with Featurevisor::createInstance([...])
• Replace use function Featurevisor\createLogger; with use Featurevisor\Logger;
• Replace createLogger([...]) with Logger::create([...])

[fahad19]

I like the direction 👍

[fahad19]

will merge and release tomorrow (Friday) 👍