`FunctionDoc` round-trip strips empty lines from Parameters and breaks doctest

numpydoc 1.9.0rc0.dev0 git tip (2025-05-16)
CPython 3.12

A round-trip through FunctionDoc improperly removes empty lines after elements of Parameters.
This in turn breaks doctest.

In [1]: def f():
   ...:     """
   ...:     Hello world
   ...:     
   ...:     Parameters
   ...:     ----------
   ...:     foo : int
   ...:         foo desc
   ...:         
   ...:         >>> x = [1, 2]
   ...:     
   ...:     bar: int
   ...:         bar desc
   ...:     """
In [2]: import doctest
In [3]: doctest.testmod()
Out[3]: TestResults(failed=0, attempted=1)
In [4]: from numpydoc.docscrape import FunctionDoc
In [5]: print(FunctionDoc(f))
.. function:: f
    


Hello world

Parameters
----------
foo : int
    foo desc
    
    >>> x = [1, 2]
bar: int
    bar desc

In [6]: f.__doc__ = str(FunctionDoc(f))
In [7]: doctest.testmod()
ValueError: line 13 of the docstring for __main__.f has inconsistent leading whitespace: 'bar: int'

Start with numpydoc.docscrape.FunctionDoc and reproduce the round-trip shown in the issue under Python 3.12. Trace how empty lines in the Parameters section are rendered, then verify that assigning the rendered text back to f.doc leaves doctest.testmod() passing without inconsistent leading whitespace.