add asgiref dep + set default timeout on page

[rmorshea]

Description

• Add asgiref as a dependency (must have been included by another package before now).
• Set default timeout on playwright page for testing - we have a IDOM_TESTING_DEFAULT_TIMEOUT, but it's not applied there.

Checklist:

Please update this checklist as you complete each item:

• Tests have been included for all bug fixes or added functionality.
• The changelog.rst has been updated with any significant changes.
• GitHub Issues which may be closed by this Pull Request have been linked.
• I have left irrelevant checklist items unchecked instead of removing them.