Trying out Pixi for image building

I'm trying out using Pixi for managing our Conda and Pypi environment in place of Mamba.

pixi-kernel replaces nb-conda-kernels to allow us to support per-project environments. 

I'm using features to capture each tutorial, then adding the tutorial feature to the default environment. The `[dependencies]` table captures our base dependencies, though we might want to refactor them out into features as well ('jupyterlab support', 'cli', 'storage', 'fast xarray',...).

You can test the lab locally with either `pixi run lab` or `docker compose up py`. 

There is one little oddity I know of right now in the pixi workflow. If you create a new directory ((like a project), `pixi init`, then following pixi commands don't target that manifest as normal. 

```
$ pixi init
Initialized project in /home/jovyan/test/.
$ pixi add fastapi
 WARN Using manifest /home/jovyan/pixi.toml from `PIXI_PROJECT_MANIFEST` rather than local /home/jovyan/test/pixi.toml
```

This is because the image has already set a `pixi shell` (well `pixi shell-hook`) to force pixi to look for a specific manifest and recorded that in an environment variable. Pixi will warn that it's using a different manifest, but its easy to screw that up.

Running `pixi shell --manifest-path ./pixi.toml` will set the pixi scope to the current environment.

```
$ pixi shell --manifest-path ./pixi.toml
 . "/tmp/pixi_env_WOz.sh"
jovyan@e5cb7d16120a:~/test$  . "/tmp/pixi_env_WOz.sh"
(test) jovyan@e5cb7d16120a:~/test$ pixi add fastapi
```

.gitignore

@@ -102,3 +102,6 @@ venv.bak/
 
 # mypy
 .mypy_cache/
+
+# Mac
+**/.DS_Store

py-base/.gitattributes

@@ -0,0 +1,3 @@
+# GitHub syntax highlighting
+pixi.lock linguist-language=YAML
+

py-base/.gitignore

@@ -0,0 +1,4 @@
+# pixi environments
+.pixi
+*.egg-info
+

py-base/Dockerfile

@@ -1,5 +1,5 @@
-#syntax=docker/dockerfile:1.3
-FROM continuumio/miniconda3:4.12.0@sha256:58b1c7df8d69655ffec017ede784a075e3c2e9feff0fc50ef65300fc75aa45ae
+#syntax=docker/dockerfile:1.7
+FROM ghcr.io/prefix-dev/pixi:0.26.1-jammy@sha256:45d86bb788aaa24d215eff57712f250329486ca8f442b91959bc9ce7ce6e053c
 
 ENV NB_USER jovyan
 ENV NB_UID 1000
@@ -10,32 +10,21 @@ ENV CONDA_ENV base
 
 # Output logging faster
 ENV PYTHONUNBUFFERED 1
-# Don't write bytecode
-ENV PYTHONDONTWRITEBYTECODE 1
 
 USER root
 RUN adduser --disabled-password --gecos "Default Jupyter user" ${NB_USER} \
-    && echo ". ${CONDA_DIR}/etc/profile.d/conda.sh ; conda activate ${CONDA_ENV}" > /etc/profile.d/init_conda.sh \
+    # && echo ". ${CONDA_DIR}/etc/profile.d/conda.sh ; conda activate ${CONDA_ENV}" > /etc/profile.d/init_conda.sh \
     && chown -R ${NB_USER}:${NB_USER} /srv
 
 WORKDIR ${HOME}
-USER ${USER}
-
-COPY ./conda-linux-64.lock /tmp/
+USER ${NB_USER}
 
-RUN --mount=type=cache,id=ohw_py,target=/opt/conda/pkgs,uid=${NB_UID},gid=${NB_UID} \
-    conda install --name ${CONDA_ENV} --file /tmp/conda-linux-64.lock && \
-    # micromamba install --name ${CONDA_ENV} --file environment.yml && \
-    find -name '*.a' -delete && \
-    # rm -rf /opt/conda/conda-meta && \
-    rm -rf ${CONDA_DIR}/include && \
-    find -name '__pycache__' -type d -exec rm -rf '{}' '+'
+COPY ./pixi.toml ./pixi.lock ${HOME}
 
-COPY CONDARC ./.condarc
-COPY --chown=${NB_USER} entrypoint.sh /opt/entrypoint.sh
+RUN --mount=type=cache,id=ohw_py,target=/home/jovyan/.cache/rattler/cache,uid=${NB_UID},gid=${NB_UID} \
+    pixi install --frozen -e default
 
-# USER root
-# RUN chown -R jovyan ${CONDA_DIR}
-USER ${NB_USER}
+RUN pixi shell-hook --frozen -e default > /srv/shell-hook.sh \
+    && echo 'exec "$@"' >> /srv/shell-hook.sh
 
-ENTRYPOINT [ "/opt/entrypoint.sh" ]
+ENTRYPOINT ["/bin/bash", "/srv/shell-hook.sh"]