fix(modules): Mailpit Container

[oliverlambson]

New Container

Fixes #626

PR Checklist

• Your PR title follows the Conventional Commits syntax
  as we make use of this for detecting Semantic Versioning changes.
• Your PR allows maintainers to edit your branch, this will speed up resolving minor issues!
• The new container is implemented under modules/*
  • Your module follows PEP 420 with implicit namespace packages
    (if unsure, look at other existing community modules)
  • Your package namespacing follows testcontainers.<modulename>.*
    and you DO NOT have an __init__.py above your module's level.
  • Your module has it's own tests under modules/*/tests
  • Your module has a README.rst and hooks in the .. auto-class and .. title of your container
  • Implement the new feature (typically in __init__.py) and corresponding tests.
• Your module is added in pyproject.toml
  • it is declared under tool.poetry.packages - see other community modules
  • it is declared under tool.poetry.extras with the same name as your module name,
    we still prefer adding NO EXTRA DEPENDENCIES, meaning mymodule = [] is the preferred addition
    (see the notes at the bottom)
• (seems to not be needed anymore) The INDEX.rst at the project root includes your module under the .. toctree directive
• Your branch is up to date (or we'll use GH's "update branch" function through the UI)

Preferred implementation

• The current consensus among maintainers is to try to avoid enforcing the client library
  for the given tools you are triyng to implement.
• This means we want you to avoid adding specific libraries as dependencies to testcontainers.
• Therefore, you should implement the configuration and the waiting with as little extra as possible
• You may still find it useful to add your preferred client library as a dev dependency

[codecov]

Codecov Report

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #625   +/-   ##
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  Coverage        ?   76.26%           
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  Files           ?       11           
  Lines           ?      573           
  Branches        ?       83           
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  Hits            ?      437           
  Misses          ?      110           
  Partials        ?       26           

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[oliverlambson]

I imagine this could be a controversial addition, since it's the first class being exported from community modules that isn't a container.

The reason I've done this is because it's a more descriptive and intuitive datatype (to me):

- users:  list[tuple[str, str]] | None
+ users:  list[MailpitUser] | None

[oliverlambson]

I've also added a py.typed as this module is fully type-hinted (see #504). Running mypy on it reveals the type hint issues in core, but raises no issues within this module