optimizing build time

- using cache
- reorder docker build steps

Dockerfile.builder

@@ -6,13 +6,13 @@ ARG API_URL
 
 # Copy local context to `/app` inside container (see .dockerignore)
 WORKDIR /app
-COPY requirements.txt .
 
-# Create virtualenv which will be copied into final container
 ENV VIRTUAL_ENV=/app/.venv
 ENV PATH="$VIRTUAL_ENV/bin:$PATH"
 RUN python3.11 -m venv $VIRTUAL_ENV
 
+COPY requirements.txt .
+
 # Install app requirements and reflex inside virtualenv
 RUN pip install -r requirements.txt