Empack 4.0.0 packing issue with jupytercad

[martinRenou]

The lite build on JupyterCAD fails with the following. This is most likely related to the latest changes on filtering:

[LiteBuildApp] ERROR | [lite] [post_build] [jupyterlite-xeus] [ERR] Object of type PosixPath is not JSON serializable
Traceback (most recent call last):
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/doit_cmd.py", line 294, in run
    return command.parse_execute(args)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/cmd_base.py", line 150, in parse_execute
    return self.execute(params, args)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/cmd_base.py", line 570, in execute
    return self._execute(**exec_params)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/cmd_run.py", line 265, in _execute
    return runner.run_all(self.control.task_dispatcher())
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/runner.py", line 254, in run_all
    self.run_tasks(task_dispatcher)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/runner.py", line 213, in run_tasks
    node = task_dispatcher.generator.send(node)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/control.py", line 629, in _dispatcher_generator
    next_step = node.step()
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/control.py", line 336, in step
    return next(self.generator)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/control.py", line 345, in _func
    for value in decorated(*args, **kwargs):
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/control.py", line 473, in _add_task
    new_tasks = generate_tasks(to_load, task_gen, ref.__doc__)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/loader.py", line 390, in generate_tasks
    for task_dict, x_doc in flat_generator(gen_result, gen_doc):
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/doit/loader.py", line 27, in flat_generator
    for item in gen:
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_core/manager.py", line 138, in _delayed_gather
    yield from _gather()
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_core/manager.py", line 131, in _gather
    raise error
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_core/manager.py", line 123, in _gather
    for task in getattr(addon, attr)(self):
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_xeus/add_on.py", line 127, in post_build
    yield from self.copy_kernels_from_prefix()
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_xeus/add_on.py", line 179, in copy_kernels_from_prefix
    yield from self.copy_kernel(kernel_dir, kernel_wasm, kernel_js)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_xeus/add_on.py", line 261, in copy_kernel
    yield from self.pack_prefix(kernel_dir=kernel_dir)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/jupyterlite_xeus/add_on.py", line 288, in pack_prefix
    pack_env(
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/empack/pack.py", line 186, in pack_env
    pack_pkg_impl(
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/site-packages/empack/pack.py", line 54, in pack_pkg_impl
    json.dump(pkg_meta, f)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/__init__.py", line 179, in dump
    for chunk in iterable:
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/encoder.py", line 325, in _iterencode_list
    yield from chunks
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/encoder.py", line 438, in _iterencode
    o = _default(o)
  File "/home/runner/micromamba/envs/build-env/lib/python3.10/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type PosixPath is not JSON serializable
static:jupyter-lite.json
.  pre_status:static:jupyter-lite.json
    tarball:         jupyterlite-app-0.2.3.tgz 9MB
    output:          /home/runner/work/JupyterCAD/JupyterCAD/lite/dist
    lite dir:        /home/runner/work/JupyterCAD/JupyterCAD/lite
    apps:            
    sourcemaps:      True
    unused packages: True