Docs CI: install gymnasium_robotics + scipy; mock rostopic

The strict-warnings sphinx-build enabled in the previous commit
surfaced real autodoc-import failures: multiros / realros import
gymnasium_robotics for goal-env support; rl_environments imports
scipy and rostopic. Without these the autodoc pages were silently
empty (warnings, but not errors in the old non-strict build).

Two fixes:

  - docs/requirements.txt: add gymnasium-robotics and scipy as
    pip deps so the imports actually succeed. Also pin gymnasium
    explicitly to 0.29.1 to match the tests-CI pin and the
    supported runtime.

  - docs/conf.py autodoc_mock_imports: add 'rostopic' (a ROS-only
    package, not pip-installable, so we mock it). Other already-
    mocked rospy ecosystem packages stay as is.

Author: ncbdrck

docs/conf.py

@@ -136,7 +136,7 @@
 # Mock them so autodoc can introspect docstrings without crashing on
 # unresolved imports.
 autodoc_mock_imports = [
-    "rospy", "rosparam", "rospkg", "xacro",
+    "rospy", "rosparam", "rospkg", "rostopic", "xacro",
     "rospy.service",
     "visualization_msgs", "geometry_msgs", "std_msgs",
     "sensor_msgs", "controller_manager_msgs",

docs/requirements.txt

@@ -6,9 +6,13 @@ sphinx-rtd-theme>=2.0
 sphinx-copybutton>=0.5
 myst-parser>=2.0
 
-# autodoc imports the four packages to read their docstrings, so they
+# autodoc imports the six packages to read their docstrings, so they
 # need to be importable from PYTHONPATH. conf.py already adds the
 # src/ trees to sys.path; this lists only the pure-Python deps the
 # packages actually pull in at import time once ROS modules are mocked.
-gymnasium>=0.29
+# Pin gymnasium to match the supported runtime (1.x removed the
+# wrapper attribute passthrough that the proxy depends on).
+gymnasium==0.29.1
+gymnasium-robotics==1.2.4
 numpy>=1.21
+scipy>=1.7