Improve config flow type hints in starline

[epenet]

Proposed change

SSIA, linked to #124316

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[home-assistant]

Hey there @Anonym-tsk, mind taking a look at this pull request as it has been labeled with an integration (starline) you are listed as a code owner for? Thanks!

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[Anonym-tsk]

LGTM

[epenet]

Note: the codecov failures are not linked to this PR.
It would be good if coverage could be improved by the code-owner in a follow-up PR.

Before:

---------- coverage: platform linux, python 3.12.3-final-0 -----------
Name                                                  Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------------------
homeassistant/components/starline/__init__.py            50     35    30%   31-92, 97-103, 108-114
homeassistant/components/starline/account.py             94     39    59%   30-32, 56, 60-78, 82, 100, 112-118, 124-130, 136-142, 147, 159, 167, 176, 186, 194
homeassistant/components/starline/binary_sensor.py       21     21     0%   3-93
homeassistant/components/starline/button.py              22     22     0%   3-57
homeassistant/components/starline/config_flow.py        105     27    74%   77, 81-84, 88-91, 140-144, 160-164, 210-221
homeassistant/components/starline/const.py               22      0   100%
homeassistant/components/starline/device_tracker.py      33     33     0%   3-63
homeassistant/components/starline/entity.py              27     27     0%   3-48
homeassistant/components/starline/lock.py                35     35     0%   3-77
homeassistant/components/starline/sensor.py              67     67     0%   3-174
homeassistant/components/starline/switch.py              38     38     0%   3-93
-----------------------------------------------------------------------------------
TOTAL                                                   514    344    33%

After:

---------- coverage: platform linux, python 3.12.5-final-0 -----------
Name                                                  Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------------------
homeassistant/components/starline/__init__.py            50     35    30%   31-92, 97-103, 108-114
homeassistant/components/starline/account.py             94     39    59%   30-32, 56, 60-78, 82, 100, 112-118, 124-130, 136-142, 147, 159, 167, 176, 186, 194
homeassistant/components/starline/binary_sensor.py       21     21     0%   3-93
homeassistant/components/starline/button.py              22     22     0%   3-57
homeassistant/components/starline/config_flow.py        104     27    74%   80, 86-89, 95-98, 147-151, 167-171, 221-232
homeassistant/components/starline/const.py               22      0   100%
homeassistant/components/starline/device_tracker.py      33     33     0%   3-63
homeassistant/components/starline/entity.py              27     27     0%   3-48
homeassistant/components/starline/lock.py                35     35     0%   3-77
homeassistant/components/starline/sensor.py              67     67     0%   3-174
homeassistant/components/starline/switch.py              38     38     0%   3-93
-----------------------------------------------------------------------------------
TOTAL                                                   513    344    33%