sudo: add mitogen_sudo_password_prompt for custom passprompt

[jettero]

@jettero:
I didn't have much to do with this. Just asked claude to fix the problem I was having with mitogen in my ansible setup. The problem turned out to be my custom sudo prompts, which I'm not willing to change, so if I wanna use mitogen, I have to fork... But feel free to reject this if you don't like it. I don't have much skin in the game.

Claude:

Mitogen's PASSWORD_PROMPT_RE matches "password" in dozens of locales, covering any default sudo configuration. But if sudoers defines a custom passprompt (e.g. [sudo] %u@%h:) that omits the word "password", mitogen never recognizes the prompt, never sends the password, and the sudo bootstrap hangs until connect_timeout.

Ansible's own sudo become plugin sidesteps this by always forcing -p, but mitogen matches the prompt on the wire instead. This commit adds a configurable regex pattern via the ansible variable mitogen_sudo_password_prompt. When set, the pattern is compiled and prepended to SetupProtocol.PARTIAL_PATTERNS, with the built-in patterns as fallback.

Configuration (group_vars, host_vars, or play vars):

    mitogen_sudo_password_prompt: '\[sudo\] \w+@[\w.]+:'

Also adds pyproject.toml so pip install -e . works with modern pip.

Thanks for creating a PR! Here's a quick checklist to pay attention to:

• Please add an entry to docs/changelog.rst as appropriate.

• Has some new parameter been added or semantics modified somehow? Please
  ensure relevant documentation is updated in docs/ansible.rst and
  docs/api.rst.

• If it's for new functionality, is there at least a basic test in either
  tests/ or tests/ansible/ covering it?

• If it's for a new connection method, please try to stub out the
  implementation as in tests/data/stubs/, so that construction can be tested
  without having a working configuration.

[moreati]

I agree with the goal, created #1503 as an umbrella for similar issues. I wan't to consider the design more - Ansible's method (set a known prompt) makes a lot of sense and is likely to be more robust.

Regardless, I can't accept this PR with failing tests and no changelog entry or docs updates.