remove asynchat/asyncore and use asyncio instead

[rerpha]

If we want to use python >=3.12 we need to remove this as it's been deprecated until then and completely removed in 3.12 onwards.

it's currently used by the stream handler, #306 says a bit about this and how we might change it to suit.

acceptance criteria

• asynchat and asyncore are removed from use in favour of asyncio
• our python testing matrix tests against 3.12 and beyond
• the pyproject.toml is updated to use >=3.10 as its python-versions

[Tom-Willemsen]

Short term fix for 3.12 could be to use a shim (https://pypi.org/project/pyasynchat/), but should still do the refactor towards standard asyncio longer term