Handle exceptions from property getters during member enumeration

[BhargavKumarNath]

Problem

When a component has a @property whose getter raises any exception
other than AttributeError, calling fire.Fire(component) crashes on
both bare invocation and --help. The raw traceback is shown instead
of usage information.

Reproducer (fire 0.7.1, Python 3.13):

import fire

class App:
    @property
    def status(self):
        raise RuntimeError("backend unavailable")
    def greet(self, who="world"):
        return f"hi {who}"

fire.Fire(App())

$ python app.py --help
RuntimeError: backend unavailable
$ python app.py # bare invocation
RuntimeError: backend unavailable
$ python app.py greet # works fine
hi world

Root Cause

inspect.getmembers in Python 3.13 tightened its internal exception
handling to only suppress AttributeError. Previously it suppressed
all exceptions from attribute getters. Fire calls inspect.getmembers
unguarded in two places during member enumeration for help rendering
and help shortcut detection.

Fix

Add GetSafeMembers to inspectutils, which mirrors the behaviour of
inspect.getmembers but catches all exceptions from attribute getters,
falling back to None for any member that raises. Replace the two
unguarded call sites in completion.VisibleMembers and
core._IsHelpShortcut with GetSafeMembers.

Members whose getters raise are preserved in the output as
(name, None), so the member name remains visible in help output
without crashing.

Testing

Three unit tests added to inspectutils_test.py:

• raising property: member present with value None
• working property: member present with correct value
• mixed properties: both cases handled correctly in one component

Full test suite: 262 passed, 2 pre-existing failures in
main_test.py unrelated to this change (Windows/Python 3.13
environment issues with regex escaping and temp file permissions).

Fixes #672