Fix Ruff FA100, I001 and UP006 errors

[hugovk]

Fix failures on main:

=================================== FAILURES ===================================
_________________________________ test session _________________________________
conftest.py:1:1: I001 [*] Import block is un-sorted or un-formatted
  |
1 | import platform
  | ^^^^^^^^^^^^^^^ I001
  |
  = help: Organize imports


_________________________________ test session _________________________________
keyring/core.py:61:55: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
   |
61 | def get_password(service_name: str, username: str) -> typing.Optional[str]:
   |                                                       ^^^^^^^^^^^^^^^ FA100
62 |     """Get password from the specified service."""
63 |     return get_keyring().get_password(service_name, username)
   |

keyring/core.py:77:34: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
   |
76 | def get_credential(
77 |     service_name: str, username: typing.Optional[str]
   |                                  ^^^^^^^^^^^^^^^ FA100
78 | ) -> typing.Optional[credentials.Credential]:
79 |     """Get a Credential for the specified service."""
   |

keyring/core.py:78:6: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
   |
76 | def get_credential(
77 |     service_name: str, username: typing.Optional[str]
78 | ) -> typing.Optional[credentials.Credential]:
   |      ^^^^^^^^^^^^^^^ FA100
79 |     """Get a Credential for the specified service."""
80 |     return get_keyring().get_credential(service_name, username)
   |

keyring/core.py:87:25: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
   |
87 | def init_backend(limit: typing.Optional[LimitCallable] = None):
   |                         ^^^^^^^^^^^^^^^ FA100
88 |     """
89 |     Load a detected backend.
   |

keyring/core.py:94:28: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
   |
94 | def _detect_backend(limit: typing.Optional[LimitCallable] = None):
   |                            ^^^^^^^^^^^^^^^ FA100
95 |     """
96 |     Return a keyring specified in the config file or infer the best available.
   |

keyring/core.py:116:47: UP006 Use `type` instead of `typing.Type` for type annotation
    |
116 | def _load_keyring_class(keyring_name: str) -> typing.Type[backend.KeyringBackend]:
    |                                               ^^^^^^^^^^^ UP006
117 |     """
118 |     Load the keyring class indicated by name.
    |
    = help: Replace with `type`

keyring/core.py:148:19: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
    |
148 | def load_env() -> typing.Optional[backend.KeyringBackend]:
    |                   ^^^^^^^^^^^^^^^ FA100
149 |     """Load a keyring configured in the environment variable."""
150 |     try:
    |

keyring/core.py:166:22: FA100 Add `from __future__ import annotations` to simplify `typing.Optional`
    |
166 | def load_config() -> typing.Optional[backend.KeyringBackend]:
    |                      ^^^^^^^^^^^^^^^ FA100
167 |     """Load a keyring using the config file in the config root."""
    |


_________________________________ test session _________________________________
tests/test_cli.py:1:1: I001 [*] Import block is un-sorted or un-formatted
   |
 1 | / import getpass
 2 | | import itertools
 3 | | import sys
 4 | | from unittest import mock
 5 | |
 6 | | import pytest
 7 | |
 8 | | from keyring import cli
 9 | | from keyring import credentials
   | |_______________________________^ I001
10 |
11 |   flatten = itertools.chain.from_iterable
   |
   = help: Organize imports

https://github.com/jaraco/keyring/actions/runs/15014236777/job/42188495940