Fix float serialization behavior in strict mode

[sydney-runkle]

Fixes this case:

from pydantic import BaseModel, Field
from typing import Union


class FloatThenInt(BaseModel):
    value: Union[float, int, str] = Field(union_mode='smart')


class IntThenFloat(BaseModel):
    value: Union[int, float, str] = Field(union_mode='smart')


float_then_int = FloatThenInt(value=100)
print(f'float then int: {float_then_int.value} {type(float_then_int.value)}')
print(float_then_int.model_dump_json())

int_then_float = IntThenFloat(value=100)
print(f'int then float: {int_then_float.value} {type(int_then_float.value)}')
print(int_then_float.model_dump_json())

Note, there may be other cases where we could fix union serialization behavior by introducing these strict checks.

Fix pydantic/pydantic#9417

[codspeed-hq]

CodSpeed Performance Report

Merging #1400 will not alter performance

_{Comparing float-ser-fix (96e84d3) with main (fd81a75)}

Summary

✅ 155 untouched benchmarks

[davidhewitt]

LGTM 👍