[rwb27]

This is the second part of the overhaul of websockets and property observations. It updates the websocket protocol to the latest version of the webthingprotocol which paves the way for sharing websockets between multiple Things.

This MR contains the following

• pydantic models describing the messages sent and received via the websocket.
• Code to relay these messages to/from the MessageBroker

Before merge:

• Use the new models in an updated websocket implementation
• Share websocket between all Things on the server.
• Test all new code

Merge checklist:

• All new/changed functions have up to date typehints and docstrings.
• Any changes to the public API have been updated in docs/src/public_api.rst.
• New or changed features have been added to (or updated in) the conceptual documentation.
• Any new or updated dependencies have been added to the project configuration (e.g., pyproject.toml).
• New functionality is fully tested.
• Any decrease in test coverage has been justified.
• Either the test-against-ofm-v3 job passes, or test-against-ofm-feature-branch passes.
• New features have been used in a branch of the OpenFlexure Microscope, which is tested in test-against-ofm-feature-branch.
  
• This code has been tested manually against simulated hardware (detail tests in "Before merge").
• This code has been tested against real hardware (detail tests in "Before merge").

[barecheck]

Barecheck - Code coverage report

Total: 96.22%

Your code coverage diff: -1.21% ▾

Uncovered files and lines

File	Lines
src/labthings_fastapi/webthing_subprotocol.py	11-13, 15, 17, 20, 27-32, 35, 38-39, 42, 45-46, 49, 52-53, 56, 63-65, 68, 71-76, 79, 87-90, 93, 96-99