fix: resolve issue where rest-numeric-enums=False is not supported

[parthea]

This PR resolves an issue where rest-numeric-enums=False was not properly supported. See test case below that fails without the fix.

(py392) partheniou@partheniou-vm-3:~/git/gapic-generator-python$ pytest /usr/local/google/home/partheniou/git/gapic-generator-python/tests/unit/generator/test_options.py
================================================================================================================================================= test session starts =================================================================================================================================================
platform linux -- Python 3.9.16, pytest-8.4.2, pluggy-1.5.0
rootdir: /usr/local/google/home/partheniou/git/gapic-generator-python
plugins: asyncio-1.2.0, anyio-4.8.0, mock-3.14.1, localserver-0.8.1, pyfakefs-5.8.0, cov-5.0.0, flaky-3.8.1
asyncio: mode=strict, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 14 items                                                                                                                                                                                                                                                                                                    

tests/unit/generator/test_options.py ...........F..                                                                                                                                                                                                                                                             [100%]

====================================================================================================================================================== FAILURES =======================================================================================================================================================
_______________________________________________________________________________________________________________________________________________ test_options_bool_flags _______________________________________________________________________________________________________________________________________________

    def test_options_bool_flags():
        # Most options are default False.
        # New options should follow the dash-case/snake_case convention.
        opt_str_to_attr_name = {
            name: re.sub(r"-", "_", name)
            for name in [
                "lazy-import",
                "old-naming",
                "add-iam-methods",
                "metadata",
                "warehouse-package-name",
                "rest-numeric-enums",
            ]
        }
    
        for opt, attr in opt_str_to_attr_name.items():
            options = Options.build("")
            assert not getattr(options, attr)
    
            options = Options.build(opt)
            assert getattr(options, attr)
    
        # Check autogen-snippets separately, as it is default True
        options = Options.build("")
        assert options.autogen_snippets
    
        options = Options.build("autogen-snippets=False")
        assert not options.autogen_snippets
    
        options = Options.build("rest-numeric-enums=False")
>       assert not options.rest_numeric_enums
E       AssertionError: assert not True
E        +  where True = Options(name='', namespace=(), warehouse_package_name='', retry=None, sample_configs=(), autogen_snippets=True, templa... 'transport', 'rest-numeric-enums', 'lazy-import', 'add-iam-methods', 'samples', 'autogen-snippets', 'gapic-version'})).rest_numeric_enums

tests/unit/generator/test_options.py:216: AssertionError
=============================================================================================================================================== short test summary info ===============================================================================================================================================
FAILED tests/unit/generator/test_options.py::test_options_bool_flags - AssertionError: assert not True
============================================================================================================================================ 1 failed, 13 passed in 0.84s