simplify multi stage dockerfile

docker/Dockerfile

@@ -1,12 +1,12 @@
 # Build stage
 FROM python:3.10-slim AS builder
-COPY . /aider
 
 RUN apt-get update && \
-    apt-get install --no-install-recommends -y build-essential git && \
-    rm -rf /var/lib/apt/lists/* && \
-    pip install --no-cache-dir /aider && \
-    rm -rf /aider
+    apt-get install --no-install-recommends -y build-essential git
+
+COPY . /aider
+
+RUN    pip install --no-cache-dir /aider
 
 # Final stage
 FROM python:3.10-slim