chore(weave): Legacy Refactor pt23

[andrewtruong]

Split out from: https://github.com/wandb/weave/pull/2182

This slice splits out:

• mypy.ini into respective trace and legacy configs
• test_weave_api -- trace and legacy tests stuck in 1 file

It also:

• Creates a copy of ref_util for trace
• Deletes remaining trace code in the legacy api.

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[andrewtruong]

closing in favor of: https://github.com/wandb/weave/pull/2272