Parallelise Dockerfile stages and enable CI layer caching

Split runtime apt-get into a separate stage so BuildKit runs it
concurrently with the builder's apt-get + pip install. Add cache_from
to the Drone CI API build step to reuse layers from the previous image.

.drone.yml

@@ -58,6 +58,7 @@ steps:
       dockerfile: crawler/Dockerfile
       context: crawler/
       auto_tag: true
+      cache_from: viktorbarzin/realestatecrawler:latest
 
   - name: Update deployment
     image: alpine

crawler/Dockerfile

@@ -1,4 +1,4 @@
-# Stage 1: Build dependencies
+# Stage 1: Install build tools and Python dependencies
 FROM python:3.13-slim AS builder
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -17,10 +17,9 @@ COPY requirements.txt ./
 RUN python -m venv /app/.venv && \
     /app/.venv/bin/pip install --no-cache-dir -r requirements.txt
 
-# Stage 2: Runtime image
-FROM python:3.13-slim
+# Stage 2: Runtime system dependencies (runs in parallel with builder)
+FROM python:3.13-slim AS runtime-base
 
-# Install only runtime system dependencies (no build tools)
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libgl1 \
     libglib2.0-0 \
@@ -29,6 +28,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libmariadb3 \
     && rm -rf /var/lib/apt/lists/*
 
+# Stage 3: Final image — combine venv from builder + runtime base
+FROM runtime-base
+
 WORKDIR /app
 
 # Copy the venv from the builder stage