Make the script engine more robust

Fixes several bugs:

* Outputs of any type convertible from NDArray (including String and
  double) were packed as images on the Python side, crashing the script.
  Now only numpy values are packed, and numpy scalars become plain numbers.
* ShmImg inputs had their shared memory closed after the script ran,
  corrupting the caller's image.
* NDArray outputs declared as Object were returned already closed.
* Non-JSON inputs (File, services, etc.) were serialized reflectively;
  now Files become paths, enums/chars become strings, and anything else
  is skipped with a warning.
* Output written via print() was silently discarded; stdout and stderr
  are now forwarded to the script context's writers.
* Tracebacks pointed at the generated wrapper script; the user script
  is now compiled with its real path, so line numbers are correct.
* Environments are now actually cached per JVM, named after the env
  file rather than the script (so scripts can share an environment),
  and built with progress reported to the status bar.
* Errors keep their causes; interrupting a script kills the worker.
* Undefined outputs no longer fail the script, and the value of the
  script's final expression is now returned.

The Python-side wrapper now lives in wrapper.py rather than being
generated by string concatenation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: ctrueden