fix: docker: fetch python deps ahead of copying in full source tree

The current build order:

 1. Copy in full source tree
 2. Fetch python build dependencies
 3. Build

The issue with this is any source tree change causes the python dependencies to
be re-fetched, then the rust components of those deps rebuilt.

Instead, copy in just the .circleci directory, which informs the python build
dependency fetch. After we have the python deps, then copy in the full source
tree and build.

Dockerfile

@@ -9,8 +9,7 @@ RUN apt update \
     && apt install --yes binutils build-essential curl pkg-config libssl-dev clang lld git patchelf protobuf-compiler zstd libz-dev \
     && rm -rf /var/lib/{apt,dpkg,cache,log}
 
-# Build influxdb3
-COPY . /influxdb3
+RUN mkdir /influxdb3
 WORKDIR /influxdb3
 
 ARG CARGO_INCREMENTAL=yes
@@ -31,6 +30,7 @@ ENV CARGO_INCREMENTAL=$CARGO_INCREMENTAL \
     PBS_VERSION=$PBS_VERSION
 
 # obtain python-build-standalone and configure PYO3_CONFIG_FILE
+COPY .circleci /influxdb3/.circleci
 RUN \
   sed -i "s/^readonly TARGETS=.*/readonly TARGETS=${PBS_TARGET}/" ./.circleci/scripts/fetch-python-standalone.bash && \
   ./.circleci/scripts/fetch-python-standalone.bash /influxdb3/python-artifacts "${PBS_DATE}" "${PBS_VERSION}" && \
@@ -38,6 +38,8 @@ RUN \
   sed -i 's#tmp/workspace#influxdb3#' "/influxdb3/python-artifacts/${PBS_TARGET}/pyo3_config_file.txt" && \
   cat "/influxdb3/python-artifacts/${PBS_TARGET}/pyo3_config_file.txt"
 
+COPY . /influxdb3
+
 RUN \
   --mount=type=cache,id=influxdb3_rustup,sharing=locked,target=/usr/local/rustup \
   --mount=type=cache,id=influxdb3_registry,sharing=locked,target=/usr/local/cargo/registry \