feat: support for evented containers as pydantic v2 fields

[tlambert03]

This is in support of #252, where I noted that evented containers don't work well as fields for pydantic models. Specifically, this enables:

class Model(pydantic.BaseModel):
    my_list: psygnal.containers.EventedList[int]  # or other evented containers

This only supports pydantic v2 (for now, and probably forever), since pydantic v1 always had very bad support for custom Generic fields

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8f44f34) to head (b239e9a).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #283   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         1864      1880   +16     
=========================================
+ Hits          1864      1880   +16     

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[codspeed-hq]

CodSpeed Performance Report

Merging #283 will not alter performance

_{Comparing tlambert03:pydantic-fields (b239e9a) with main (8f44f34)}

Summary

✅ 66 untouched benchmarks