feat(bindings/python)!: Implement File and AsyncFile to replace Reader

[Xuanwo]

Python users don't know about reader and writer, they are using File-like objects and context manager.

This PR add Operator::open and AsnycFile to make our API more native to python users.

Async version:

async with await op.open(filename, "rb") as r:
    content = await r.read()

Blocking version:

with op.open(filename, "rb") as r:
    content = r.read()

Writer is also supported in the same way:

async with await op.open(filename, "wb") as w:
    await w.write("Hello, World!")

Close #2570

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Only wb and rb supported so far.

[Zheaoli]

Mostly LGTM

Here may be something to follow up

1. In Python, People may use r+b to use read and write API in the same object
2. We may need test for context manager

[Xuanwo]

In Python, People may use r+b to use read and write API in the same object

This is not allowed in opendal. We can't and don't want to support this use case.