8.0.0: Update to Python 3.12, new API, new code and Ubuntu 24.10 (#16)

• Synchronize version number up with major API release in Mathics Kernel
• Add dmathics3-tokens interface to mathics3-tokens (from mathics-scanner)
• Use newer versions of everything, Ubuntu, Python, SymPy, etc.
• Remove lots of copies of old wheels from the source; we can now get everything reasonably fast from inside docker