This patch improves our type hints for ".filter()" to work with
"typing.TypeGuard". For example:

from typing import TypeGuard

from hypothesis import strategies as st

def is_str(x: object) -> TypeGuard[str]:
return isinstance(x, str)

s = st.from_type(object).filter(is_str)

previously: SearchStrategy[object]

now: SearchStrategy[str]

reveal_type(s)

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