Support mypy 1.11

[Redoubts]

A couple changes force some fixes in the plugin,

https://github.com/python/mypy/pull/17304 took out an arg from UninhabitedType, and https://github.com/python/mypy/pull/17311 introduced TypeVarIds

I ran the tests, but let me know if there's anything else I should consider. I understand that newer trio versions make this plugin obsolete, but my code isn't there yet.

fixes #95

[jakkdl]

out of curiosity, what is it that blocks you from bumping trio versions? If this is widespread maybe we might reluctantly keep this repo alive even after mypy adds the feature which makes it fully redundant on newer trio.

[Redoubts]

I took a second look, and the trio.MultiError deprecation isn't as hard as I thought it would be. I'm less invested in this change, tho someone else may still want it.