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

[crusaderky]

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'