readthedocs: solely use requirements.in/txt

- Use reproducible build pattern as advised in the buildthedocs docs.

docs/requirements.in

@@ -0,0 +1,5 @@
+breathe==4.35.0
+readthedocs-sphinx-search==0.1.1
+sphinx==5.3.0
+sphinxcontrib.blockdiag==3.0.0
+sphinx_rtd_theme==1.1.1

docs/requirements.txt

@@ -1,44 +1,74 @@
-alabaster==0.7.12
-Babel==2.11.0
+#
+# This file is autogenerated by pip-compile with Python 3.11
+# by the following command:
+#
+#    pip-compile docs/requirements.in
+#
+alabaster==0.7.13
+    # via sphinx
+babel==2.12.1
+    # via sphinx
 blockdiag==3.0.0
-breathe==4.33.0
-brotlipy==0.7.0
+    # via sphinxcontrib-blockdiag
+breathe==4.35.0
+    # via -r docs/requirements.in
 certifi==2023.7.22
-cffi==1.15.1
-charset-normalizer==2.1.1
-colorama==0.4.6
-cryptography==41.0.3
-docutils==0.17
+    # via requests
+charset-normalizer==3.2.0
+    # via requests
+docutils==0.17.1
+    # via
+    #   breathe
+    #   sphinx
+    #   sphinx-rtd-theme
 funcparserlib==1.0.1
+    # via blockdiag
 idna==3.4
+    # via requests
 imagesize==1.4.1
-importlib-metadata==4.11.4
-Jinja2==3.1.2
-MarkupSafe==2.1.1
-mpi4py==3.1.3
-numpy==1.22.0
-packaging==22.0
-Pillow==9.4.0
-pip==22.3.1
-pycparser==2.21
-Pygments==2.15.0
-pyOpenSSL==23.0.0
-PySocks==1.7.1
-pytz==2022.7
+    # via sphinx
+jinja2==3.1.2
+    # via sphinx
+markupsafe==2.1.3
+    # via jinja2
+packaging==23.1
+    # via sphinx
+pillow==10.0.0
+    # via blockdiag
+pygments==2.16.1
+    # via sphinx
+readthedocs-sphinx-search==0.1.1
+    # via -r docs/requirements.in
 requests==2.31.0
-setuptools==65.6.3
+    # via sphinx
 snowballstemmer==2.2.0
-Sphinx==4.5.0
-sphinx-rtd-theme==1.0.0
-sphinxcontrib-applehelp==1.0.2
+    # via sphinx
+sphinx==5.3.0
+    # via
+    #   -r docs/requirements.in
+    #   breathe
+    #   sphinx-rtd-theme
+    #   sphinxcontrib-blockdiag
+sphinx-rtd-theme==1.1.1
+    # via -r docs/requirements.in
+sphinxcontrib-applehelp==1.0.4
+    # via sphinx
 sphinxcontrib-blockdiag==3.0.0
+    # via -r docs/requirements.in
 sphinxcontrib-devhelp==1.0.2
-sphinxcontrib-htmlhelp==2.0.0
+    # via sphinx
+sphinxcontrib-htmlhelp==2.0.1
+    # via sphinx
 sphinxcontrib-jsmath==1.0.1
+    # via sphinx
 sphinxcontrib-qthelp==1.0.3
+    # via sphinx
 sphinxcontrib-serializinghtml==1.1.5
-typing_extensions==4.4.0
-urllib3==1.26.13
-webcolors==1.12
-wheel==0.38.4
-zipp==3.11.0
+    # via sphinx
+urllib3==2.0.4
+    # via requests
+webcolors==1.13
+    # via blockdiag
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools

readthedocs.yml

@@ -1,12 +1,10 @@
 # .readthedocs.yml
 version: 2
 
-conda:
-  environment: docs/environment.yml
-
 python:
-   version: 3.7
-   system_packages: true
+   version: 3.8
+   install:
+       - requirements: docs/requirements.txt
 
 formats:
   - pdf