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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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[bot]]

CodSpeed Performance Report

Merging #283 will not alter performance

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

Summary

✅ 66 untouched benchmarks