feat: Add .binder directory with config files

* For reproducibility dynamically create the environment from the Pixi
  lock file that uses postBuild and runtime.txt.
* Move apt.txt under .binder/ directory

Author: matthewfeickert

apt.txt .binder/apt.txtapt.txt renamed to .binder/apt.txt

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+set -ex
+
+# Install Pixi
+curl -fsSL https://pixi.sh/install.sh | sh
+echo 'eval "$(pixi completion --shell bash)"' >> ~/.bashrc
+. ~/.bashrc
+# Sourcing ~/.bashrc doesn't seem to pick up changes, so manually set PATH
+export PATH="~/.pixi/bin:${PATH}"
+
+# Export workspace to conda explicit spec
+pixi workspace export conda-explicit-spec --platform linux-64 .binder/
+
+# Install environment
+mamba install --name notebook --file .binder/default_linux-64_conda_spec.txt

.binder/postBuild

@@ -0,0 +1 @@
+python-3.13