docker: Fix python venv setup

- Copy python libraries from venv source location
- Activate venv in all RUNs separatly because each RUN is executed in a new shell, so the environment changes do not persist between RUN commands.

Dockerfile

@@ -279,16 +279,16 @@ RUN mkdir -p /root/.venvs && \
 COPY --from=builder /tmp/rustup_install_opts.txt /tmp/rustup_install_opts.txt
 # Setup ENV $RUSTUP_INSTALL_OPTS for this stage
 RUN export $(cat /tmp/rustup_install_opts.txt)
-ENV PATH="/root/.cargo/bin:/root/.venvs/cln/bin:$PATH"
+ENV PATH="/root/.cargo/bin:/root/.venvs/cln/lib:$PATH"
 RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y ${RUSTUP_INSTALL_OPTS}
 
 WORKDIR /opt/lightningd/plugins/clnrest
 COPY --from=builder /opt/lightningd/plugins/clnrest/requirements.txt .
-RUN pip3 install -r requirements.txt
+RUN . /root/.venvs/cln/bin/activate && pip3 install -r requirements.txt
 
 WORKDIR /opt/lightningd/plugins/wss-proxy
 COPY --from=builder /opt/lightningd/plugins/wss-proxy/requirements.txt .
-RUN pip3 install -r requirements.txt
+RUN . /root/.venvs/cln/bin/activate && pip3 install -r requirements.txt
 RUN pip3 cache purge
 
 WORKDIR /opt/lightningd
@@ -323,7 +323,7 @@ RUN --mount=type=bind,from=builder,source=/var/libpq,target=/var/libpq,rw \
     ldconfig
 
 COPY --from=builder /tmp/lightning_install/ /usr/local/
-COPY --from=builder-python /usr/local/lib/python3.11/dist-packages/ /usr/local/lib/python3.11/dist-packages/
+COPY --from=builder-python /root/.venvs/cln/lib/python3.11/site-packages /usr/local/lib/python3.11/dist-packages/
 COPY --from=downloader /opt/bitcoin/bin /usr/bin
 COPY --from=downloader /opt/litecoin/bin /usr/bin
 COPY tools/docker-entrypoint.sh entrypoint.sh