preserve Parameter subclass when copying Parameters

[imnotgonnasithereandtryallday]

Description

If an instance of a type derived from Parameter is added to a Parameters instance,
and the Parameters instance is then copied, the copy contains a parameter of type Parameter.
This PR changes the contained parameter type to the derived one.

I moved the code copying Parameter instances to Parameter.__deepcopy__ so that the derived class can adds attributes.
This should not break any existing code unless someone uses __deepcopy__ for something else than copying.

Type of Changes

• Bug fix

Tested on

Python: 3.9.13
lmfit: 0.0.post2850+gb250ed7.d20240807,
scipy: 1.13.1,
numpy: 2.0.0,
asteval: 1.0.2,
uncertainties: 3.2.2

Verification

• included docstrings that follow PEP 257?
• referenced existing Issue and/or provided relevant link to mailing list?
  No, I have not opened nor found a relevant Issue.
• verified that existing tests pass locally?
  Tests do not pass, but the result is the same as on the master branch (the added test passes).
  FAILED tests/test_parameters.py::test_check_ast_errors - Failed: DID NOT RAISE <class 'NameError'>
  1 failed, 650 passed, 12 skipped, 6 warnings in 127.66s (0:02:07)
• verified that the documentation builds locally?
  Does not build:
  Extension error:
  Could not import extension sphinx.builders.epub3 (exception: cannot import name 'jsonimpl' from partially initialized
  module 'sphinxcontrib.serializinghtml' (most likely due to a circular import)
• squashed/minimized your commits and written descriptive commit messages?
• added or updated existing tests to cover the changes?

[newville]

@imnotgonnasithereandtryallday what problem does this solve?

Do we say somewhere that we support using objects derived from Parameter? Parameter has a generic user_data attribute for adding data. Is there a compelling use case for supporting more than that?

I have not looked at the test failures. But version 1.3.2 does pass all tests.