Update FileIO comments, documentation to match implementation

Documentation

Discuss thread: https://discuss.python.org/t/change-open-write-to-guarantee-all-bytes-will-be-written-or-an-exception-will-be-thrown/71082

1. FileIO behaves differently than its code comments around read and readall. Update the code comments to match current behavior
   • PEP 475, reads are retried in some cases
   • .readall() makes multiple system calls by design
2. Add documentation to open() builtin that buffering=0, which currently just says "disables buffering") changes how .write() behaves and may result in data loss as a result of a partial write (ex. gh-126606).
   • TextIO and BufferedIO (which are gotten via commonly used open('README.rst'), open('README.rst', 'rb')) retry partial writes providing a user a guarantee either all bytes will be written or an exception will be thrown.
   • FileIO is "Raw I/O" and by PEP-3116 design, as documented, and currently implemented does not retry partial writes.
   • Most the time, buffering=0 currently speeds up writing a file, but it can also result in corrupted files, ex. gh-126606 from using FileIO directly
   • I would like to try and change the behavior of buffering=0 to use BufferedIO but with a 0 sized buffer, and that is on my roadmap but will be a while (people use the flag for a reason / get benefit!). This will mean open() always returns an object which implements "Write all or throw exception" behavior.
   • Add warning / document existing behavior on open() in the meantime.

Linked PRs

• gh-129012
• gh-135328
• gh-150957
• gh-150958
• gh-150959

Bắt đầu bằng cách xem xét các chú thích trong mã FileIO và tài liệu về builtin open() được liên kết trong issue, sau đó kiểm tra các PR được liên kết gh-129012, gh-135328, gh-150957, gh-150958 và gh-150959. Công việc được xem là hoàn tất khi các chú thích mô tả hành vi hiện tại của read/readall và tài liệu về open() giải thích rõ buffering=0 cùng hành vi mất dữ liệu khi ghi một phần.