Python 3.14 compatibility

[JostMigenda]

Using checklist from #10:

• Read through “What’s New in Python 3.x” document to look for major changes that require changes to the content of the course (e.g. new features like free-threading, JIT, …)
  • free-threading and JIT are still off by default, so okay not to include them yet
  • concurrent.futures.InterpreterPoolExecutor is new, which combines advantages of ThreadPoolExecutor and ProcessPoolExecutor, so might be a good recommendation once we add more on parallelism
  • otherwise I spot nothing that has significant impacts on the course, but some nice quality of life improvements (e.g. better error messages, syntax highlighting in the REPL)
• Run through code snippets and make sure they run without deprecation warnings, etc.
• Verify that performance claims remain qualitatively correct. (Some quantitative variations between different machines or CPython versions are expected.)
• Check that dependencies (e.g. NumPy, line_profiler, …) have published wheels supporting the new release.
  • Most are ready. line_profiler does not yet have binary wheels on PyPI (hopefully soon!); I had no issues building from sdist on my Mac, but learners should probably stick with 3.13 for now, to be safe.