* Fix TextCanvas `CanvasError("Attribute extends beyond text...")

* `[[]] * ...` causes
  list of 1 list with pointers
  amount equal to multiplier
  instead of "list of lists"
* Add 2 basic font tests which check for Canvas create issue
* Add few type annotations during debug process

Fix: #554

* Force tests to restore default encoding in tearDown

Tests order change should not cause tests failures

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* Return original code to the deprecated getters and setters

* Make more aggressive deprecation warning

Fix: #548

* Return original code to the deprecated getters and setters

* Make more aggressive deprecation warning

Fix: #548

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* Fix incorrect type cast in vterm (`apply_mapping` should return `bytes`)

Add `time.sleep(0.1)` to the event loop tests:
  in the worst scenario on windows and slow machine
  function in parallel thread/async can wait up to 80 milliseconds (tested)
Add type annotations to the `vterm` and `test_vterm` to simplify error lookup.
* Fix `DeprecationWarning` in doctests & examples
* Add `pytest` configuration in `pyproject.toml` without migration
* `Signals.emit()` rework: stop `user_args` join with `weak_args`

Partial: #544
Partial: #512
Partial: #406

* drop `sleep`: not enough effective with pytest

* set timer for errors raise to 0: faster raise, faster test done

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* Fix text layout for `align="center", wrap="clip"`

- Fix: Prevent zero run length in text layout.

Refs: urwid#542

* Add test for "clip" text layout fix

Refs: #542

* [BREAKING CHANGE] Fix: #90 Remove idle emulation from asyncio event loop

Re-implement abandoned PR #418
* Fix "not hashable `AttrSpec`" and it's instance creation price (use `__slots__`)
  `AttrSpec` instances may be created in huge amount,
  with slots this process consume less resources.
* `Terminal` is always created with event loop,
  if not provided -> `SelectEventLoop` is used
* Fixed `TornadoEventLoop` & `AsyncioEventLoop` logic
  (Tornado IOLoop is asyncio based)

For extra details see original PR.

* Make `AttrSpec` immutable and hash-reusable

* Update IDLE callback comment

* Update urwid/display_common.py

Co-authored-by: Ian Ward <ian@excess.org>

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>
Co-authored-by: Ian Ward <ian@excess.org>

* [BREAKING CHANGE] Refactoring: Split event loop in several modules

* `urwid.main_loop` is split into multiple modules which is easier to maintain
* `urwid.compat` is not used anymore and removed
* `TornadoEventLoop`, `GLibEventLoop`, `TwistedEventLoop` and `TrioEventLoop`
  accessible ONLY if required dependencies installed
  (like: Tornado installed -> `TornadoEventLoop` is accessible for import)
* `TornadoEventLoop` use the same idle logic as `AsyncioLoop`:
  tornado.ioloop.IOLoop is asyncio based.
* Trio < 0.15 is not supported. Version 0.15 was released almost 3 years ago.
* Tornado < 5.0 is not supported. Tornado 5.0 was released 5 years ago.

* Remove useless shebang

* `EventLoop` should be real abstract
* add new module docstrings

* Fix docstrings

* remove unneeded import

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* not switching to Unicode-only at this moment, so make simple

Fix #408

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* If body is not `Sized` - `__len__` call should raise `AttributeError`
* Downside: since body can be replaced, `__len__` is always set ant `ListBox` by itself will pass `Sized` instance check
* Relax `SimpleListWalker` constructor rules: any Iterable is allowed as source due to `list` is used internally

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

* Deprecate legacy property creation

* Drop long time ago removed methods (never returning methods)
* Move large part of property implementations under `@property`
* Emit `PendingDeprecationWarning`
  for old compatibility code
  for public methods used as core for property and methods for compatibility
* Emit `DeprecationWarning`
  for private methods used in property construction
  using `property()` call

Due to amount of copy-paste like changes, for containers shared part is moved to the existing base classes
Add `__len__` to the list based containers. Related #445
Fix typo in type annotation for `Frame.mouse_event`

* Update urwid/canvas.py

Co-authored-by: Ian Ward <ian@excess.org>

* Update urwid/canvas.py

Co-authored-by: Ian Ward <ian@excess.org>

* Update urwid/tests/test_container.py

Co-authored-by: Ian Ward <ian@excess.org>

* Fix typo in test name

* Frame `header`, `body` and `footer` also has property and methods from pre-property era

Make consistent with other containers

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>
Co-authored-by: Ian Ward <ian@excess.org>