Visualizer: a statement call of your own function ends as None - #59

P49. Until now, a call that is a whole statement and returns None kept its call text as its last step. That hid what a function without a matching return gives.

Rule (_eval_call, _glpython_is_own_function in src/runtime/visualizer.py), the same for a line of the program, a REPL input and a doctest example:

• The learner's own function → None. That means a _GlpythonFunction (a def or lambda the visualizer traces), or a function whose code comes from a project file (/<path>), from code the visualizer compiled itself (<glpython>, e.g. methods of a class), or from an earlier REPL input (<repl>). This also covers functions of the project's other files, which stay opaque in a REPL or doctest trace.
• Everything else keeps its call text: built-ins, methods of built-in types, and functions from modules that come with Python or glpython (print(...), xs.append(1), random.shuffle(xs), gturtle.forward(10)).
• Calls whose value is used show None as before. The console is unchanged: nothing for None, as in CPython's REPL.

Example: anwenden('*', 3, 4) without a case for '*':

• Test run: the failing example's last step is None, with «Erhalten: (Keine Ausgabe) · Erwartet: 12» below it.
• Shell and program line: they end on None.
• «Baum»: the node becomes None, as for a call whose value is used.

Checks:

• scripts/check-runtime-none-calls.py (new, in test:runtime), which fails on the old code:
  • a program with an own function, a function of another file, a lambda, a method of the learner's class, a function under another name, print, append, random.shuffle, gturtle;
  • a REPL input and a doctest example (traced against the REPL's and the Tests run's namespace): own function with and without print, a function from an earlier REPL input, print, a value;
  • the console prints nothing for None.
• check-console-browser.mjs, for each of Kasten, Ersetzung and Baum, in Chrome with Pyodide:
  • a line of the program ends as None, while print/append keep their text;
  • a REPL input ends as None and the console shows nothing;
  • the failing example ends as None with «Erhalten» below it.
• The print-instead-of-return hint and passing examples: doctests.py is untouched, and check-runtime-doctests.py passes.
• README (a paragraph under the visualizer) and CLAUDE.md updated; the code comments rewritten.

Going live:

• Merging deploys the embed to Pages, so the courses get it right away (no macro change).
• For the IDE: tag v0.1.33, then bump the IDE.

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