fix: add missing faiss-cpu dependency to requirements.txt

[Pratyush-Panda-2006]

fixes #1663

What Was Done
Created New Branch: Checked out the main branch, pulled the latest changes, and created a new branch fix/issue-1663.
Added Missing Dependency: Added faiss-cpu>=1.7.4 to
requirements.txt
to resolve the missing dependency for two_tower_retrieval.py and test_neural_retrieval.py.
Verified Functionality:
Installed faiss-cpu in the local environment and ran the tests.
Verified that tests/test_neural_retrieval.py now runs and passes successfully:
bash

pytest tests/test_neural_retrieval.py

[github-actions]

🎉 Welcome to Hybrid Recommender, @Pratyush-Panda-2006! This is your first contribution here!

Labels added: gssoc:approved | mentor:leonagoel | status:review-needed

PR Description Checklist:

NO - What changed section
NO - Why section
NO - How to test section
YES - Related issue linked

⚠️ Some required sections are missing. Please update your PR description.

What happens next:

1. @leonagoel will review your changes
2. CI checks must pass
3. Once approved, this PR will be auto-merged

⏱️ Please respond to review comments within 48 hours.