Remove accidental playwright dependency

[Archmonger]

Current Situation

In 1.0.0 we are importing from .testing.backend import _hotswap, _MountFunc within idom.widgets. This was a bad idea since the import stack now forces users to have to install playwright.

User environments aren't going to have playwright installed.

  File "C:\Users\Markg\Documents\Repositories\Conreq\conreq\config\__init__.py", line 1, in <module>
    from conreq.config.types import (
  File "C:\Users\Markg\Documents\Repositories\Conreq\conreq\config\types.py", line 8, in <module>
    from idom.html import div, span
  File "C:\Users\Markg\Documents\Repositories\Conreq\.venv\lib\site-packages\idom\__init__.py", line 1, in <module>
    from idom import backend, config, html, logging, sample, svg, types, web, widgets
  File "C:\Users\Markg\Documents\Repositories\Conreq\.venv\lib\site-packages\idom\widgets.py", line 13, in <module>
    from .testing.backend import _hotswap, _MountFunc
  File "C:\Users\Markg\Documents\Repositories\Conreq\.venv\lib\site-packages\idom\testing\__init__.py", line 3, in <module>
    from .display import DisplayFixture
  File "C:\Users\Markg\Documents\Repositories\Conreq\.venv\lib\site-packages\idom\testing\display.py", line 7, in <module>
    from playwright.async_api import (
ModuleNotFoundError: No module named 'playwright'

Proposed Actions

Either completely remove hotswap (to be honest, I don't think anyone other than IDOM Core currently uses it), or do some lazy imports for _hotswap and manually define the type hint.