v3.1.0 — Failure Context in Logfiles, PEP 561, Docs Refresh

✨ New Features

Failure context in task logfiles: when a task fails, its logfile now
includes the same structured information shown in the HTML failure email —
function name, args/kwargs, downstream impact, traced-vars location, and
the traceback — not just the bare exception message and stack trace.

Introduced _ErrorData, a typed view over the internal task_context
payload, and _ErrorContextFormatter, a shared base class for the email
and logfile formatters. Both formatters now read one typed object instead
of independently pulling fields out of an untyped dict.
Extracted plain-text logfile rendering into a new _log_formatting module
(_TaskLogFormatter), keeping _email_internals focused on SMTP/HTML
concerns only.

Added PEP 561 support: shipped py.typed marker and the
"Typing :: Typed" classifier, so downstream mypy/pyright runs pick up
this package's type hints.
Removed the stale version_files entry from [tool.commitizen] (version
is sourced from git tags via hatch-vcs).
Refined the package description to lead with what the library does and
call out that tasks are plain callables.

Configured mkdocstrings for NumPy-style docstrings (docstring_style: numpy) and enabled heading/signature rendering — the API Reference page
now shows class names, method sections, and proper parameter/attribute
lists instead of flat paragraphs.
Updated the "Customizing the HTML email" section and Quick Start example
to use SMTPConfig/HTMLEmailStyle (the old HTMLSMTPHandler references
were stale after the v3.0.0 API change).
Added a "Retries & Timeouts" section to the advanced example, documenting
timeout, retries, and retry_on.

Bumped actions/checkout and astral-sh/setup-uv to their latest
available major tags (v6) across all workflows to silence Node 20
deprecation warnings.