feat(quivr-core): beginning (#3388)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

.github/workflows/backend-core-tests.yml

@@ -3,10 +3,10 @@ name: Run Tests with Tika Server
 on:
   push:
     paths:
-      - "backend/core/**"
+      - "core/**"
   pull_request:
     paths:
-      - "backend/core/**"
+      - "core/**"
   workflow_dispatch:
 
 jobs:
@@ -30,7 +30,7 @@ jobs:
           working-directory: backend
       - name: 🔄 Sync dependencies
         run: |
-          cd backend
+          cd core
           UV_INDEX_STRATEGY=unsafe-first-match rye sync --no-lock
 
       - name: Run tests
@@ -40,7 +40,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y libmagic-dev poppler-utils libreoffice tesseract-ocr  pandoc
-          cd backend
+          cd core
           rye run python -c "from unstructured.nlp.tokenize import download_nltk_packages; download_nltk_packages()"
           rye run python -c "import nltk;nltk.download('punkt_tab'); nltk.download('averaged_perceptron_tagger_eng')"
           rye test -p quivr-core