Implement Core Engine Entry Point (Training & Multi-Mode Inference) (#7)

# Description
This PR introduces the primary entry point for the QUADTRIX engine in
src/main.cpp. It establishes a unified workflow that handles model
lifecycle management without relying on TorchScript, utilizing our
custom internal headers for model architecture.

# Key Features
- Dual-Mode Execution: Integrated support for both a training loop and
an interactive chat mode.

- Infinite Generation: Implemented an unconstrained inference loop for
continuous text generation.

- C++ Architecture: Bypasses TorchScript to use custom-defined layers
and headers, ensuring direct control over the execution graph.

- Resource Management: only for CPU

Author: codeaddict-119