perf(python): get object __dict__ for faster field read/write

[chaokunyang]

What does this PR do?

This PR extract __dict__ in object when serialize a dataclass without slots for faster attribute set/set by 16%

Related issues

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

Benchmark

For following object:

COMPLEX_OBJECT = ComplexObject1(
    f1=ComplexObject2(f1=True, f2={-1: 2}),
    f2="abc",
    f3=["abc", "abc"],
    f4={1: 2},
    f5=2**7 - 1,
    f6=2**15 - 1,
    f7=2**31 - 1,
    f8=2**63 - 1,
    f9=1.0 / 2,
    f10=1 / 3.0,
    f12=[-1, 4],
)

This PR gives a 16% speed up

[chaokunyang]

cc @penguin-wwy

[pandalee99]

LGTM,thanks~