jw.pkg: Fix "make check" static code check fallout

The previous commits have put rules for linting and formatting via
ruff, yapf, mypy and pyright into place. They are checked with the
make check target, and this commit adds the fixes for the target to
succeed.

It does some refactoring where type checking dug up dirty bits, and
also adds lots of churn in the Python code. To a good deal, that's
owed to mere formatting changes. It would have been better to
seperate those from syntax and refactoring fixes into multiple
commits, so that the interesting changes don't drown in the
formatting nose. However, that would have been a lot of additional
work only to be thrown away by later commits, hence this commit has a
big diff in one piece. The size of the diff is regrettable but
hopefully a one-off: What it buys is automatic format checking for CI
and predictble formats for smaller diffs in the future.

Rules that "make check" enforces are, in the following order

   - Syntax checkers:

      - ruff check .
      - mypy .
      - pyright

   - Format check:

     - yapf --diff --recursive .

The refactoring includes:

  - Turn the Result class into a more elaborate object, capable of
    doing more heavy lifting around stderr and stdout decoding,
    summarizing outcome, and matching error strings.

    Aside from fixing broken type checks, this also removes lots of
    boilerplate calling code which is currently used for handling
    possible call outcome scenarios. Trying to access an inexistent,
    decoded string should raise a meaningful exception by itself now,
    which removes lots of code with case distinctions.

  - Fix Cmd type hierarchy:

    - Add the AbstractCmd class above Cmd. This is necessary because
      the checker rightfully complains it can't instantiate a Cmd
      instance where constructor arguments were needed. They never
      were, but the type used at the instantiating code's location in
      jw.pkg.App so claims.

    - Lots of sub- and sub-subcommands are derived from the base
      class of the invoking command. That provides some properties
      shared across the ancestor hierarchy of a command, but is
      semantically unsound. Fix that by introducing jw.pkg.BaseCmd
      class as a place to provide basic helpers shared across all
      commands used in a jw.pkg.App's context, and derive all command
      classes from that afresh. The parent command is still reachable
      via a common parent property.

Formatting changes are conforming to PEP-8, mostly, with minor
tweaks. All in all they include the following changes.

  - Remove # -*- coding: utf-8 -*-

    The line was needed by Python 2 which is not supported anylonger.
    For Python 3, the default encoding is UTF-8, anyway.

  - Allow to run "make py-format" without having it produce any
    changes. It's basically "yapf --in-place --recursive ." with some
    code style settings, see conf/topdir/pyproject.toml. The settings
    may be debatable. I've had custom tweaks in place on that target,
    too, but then again, IDEs would have more hassle to integrate
    that.

  - Introduce a 88 character line length limit

  - One import per line, reshuffle them semantically, see
    [tool.isort] in pyproject.toml.

  - Hide imports needed for type-checking only behind

      if TYPE_CHECKING

  - Spaces around assignments accounts for much churn. Having having
    no spaces in inline parameter list assignments and default
    parameter values would arguably be more compact where it's
    useful. On the other hand, I have not found a code formatter
    which allows spaces around assignments in parameter lists broken
    into one per line and that's often better than a wall of text.

  - Add two spaces before # export, as this seems to be mandated by
    PEP-8

  - Use single quotes by default

Signed-off-by: Jan Lindemann <jan@janware.com>

scripts/jw-pkg.py

@@ -1,5 +1,4 @@
 #!/usr/bin/python3
-# -*- coding: utf-8 -*-
 # PYTHON_ARGCOMPLETE_OK
 
 from jw.pkg.App import App