Add RepLLaMA Retreiver – Verify Implementation Matches Paper

We are integrating the RepLLaMA model for inference-only use, based on the official implementation:

🔗 https://github.com/texttron/tevatron/tree/main/examples/repllama

📄 Paper: RepLLaMA: Fine-Tuning LLaMA for Multi-Stage Text Retrieval
https://arxiv.org/abs/2310.08319

This milestone tracks the following tasks:

1. Add RepLLaMA inference module

2. Ensure input formatting and scoring follow the original setup

3. Confirm correct LLaMA weight usage (e.g., LoRA if applicable)

4. Plan to evaluate results later against reported benchmarks