lisa.utils: Fix inspect.getsource() for newtype() in Python 3.13

FIX

Python 3.13 inspect.getsource() uses the new __firstlineno__ attribute
that allows getting the first line number of the class declaration.
Unfortunately, this was set to the location inside newtype where the
class is actually created, leading to problems in Sphinx autodoc.

Set the __firstlineno__ attribute manually to the newtype() caller's
location to preseve accurate source location.