feat(sapphire): use of SharedArrayBuffer requires cross-origin isolation

feat: raise AdapterError if provided harness file is empty

feat(fenix_target): update to support fxpoppet changes

feat(fenix_target): update to support fxpoppet changes

Add support for running additional services (#484)

* wip: initial attempt at adding webtransport to grizzly

* refactor: use future annotations and remove Optional type

* refactor: add explicit imports for os methods

* docs: remove unnecessary type defintion from docstring

* fix: move pathlib import into type checking block

* fix: a few more minor nits

* docs: add explanation for over-riding wpt _doc_root global

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Co-authored-by: Tyson Smith <tyson.w.smith@gmail.com>

fix(tests): update mocking in cache tests

fix: use more generic types in Target

feat!: replace --headless with --display

fix(sapphire): unquote() is now able to handle bytes

docs: update usage docs