✨ Support dataclasses in responses

[tiangolo]

✨ Support dataclasses in responses, e.g.:

from typing import List, Optional

from fastapi import FastAPI

from pydantic.dataclasses import dataclass

app = FastAPI()


@dataclass
class Item:
    name: str
    price: Optional[float] = None
    owner_ids: Optional[List[int]] = None


@app.get("/items/foo")
def get_item():
    return Item(name="foo", price=1.0, owner_ids=[1, 2, 3])

This is a continuation of #2722. I do it in a new branch because I'm not allowed to push commits to the branch in the original PR.

I added extra tests covering other cases, when not using response_model, and added/fixed support for them.

[codecov]

Codecov Report

Merging #3576 (7ccad39) into master (fa7e3c9) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master     #3576    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          246       248     +2     
  Lines         7591      7746   +155     
==========================================
+ Hits          7591      7746   +155     

Impacted Files	Coverage Δ
fastapi/encoders.py	100.00% <100.00%> (ø)
fastapi/routing.py	100.00% <100.00%> (ø)
tests/test_serialize_response_dataclass.py	100.00% <100.00%> (ø)
tests/main.py	100.00% <0.00%> (ø)
fastapi/utils.py	100.00% <0.00%> (ø)

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[github-actions]

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