Fix JSON encoding/schema of pydantic v1 models

[alexmojaki]

Closes #147

Tested manually by install pydantic v1 and running:

import pydantic


class Foo(pydantic.BaseModel):
    bar: int
    baz: str


import logfire

logfire.configure(console=logfire.ConsoleOptions(verbose=True))

logfire.info('hi', foo=Foo(bar=1, baz='a'))

Automatic testing will require actually installing pydantic v1 in CI which is challenging. The tests fail to start in various ways with v1 installed. Using pydantic.v1 with v2 installed doesn't reproduce the original problem.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!