fix ReadTheDocs: show pre-run notebook plots without re-execution

Set nbsphinx_execute = "never" so nbsphinx uses existing cell outputs
instead of trying to re-run notebooks, and add pandoc as an apt package
in readthedocs.yaml since nbsphinx requires it for notebook conversion.

Author: katosh

docs/source/conf.py

@@ -70,6 +70,9 @@
 # This pattern also affects html_static_path and html_extra_path.
 exclude_patterns = ["_build", "**.ipynb_checkpoints"]
 
+# Use pre-executed notebook outputs; never re-run on the build server
+nbsphinx_execute = "never"
+
 
 # -- Options for HTML output -------------------------------------------------
 

readthedocs.yaml

@@ -4,6 +4,8 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
+  apt_packages:
+    - pandoc
 
 sphinx:
    configuration: docs/source/conf.py