[abhishekcpp007]

What does this PR do?

Capturing swaps sys.stdout for a plain StringIO while a candidate solution runs, and the LCB grader reads the solution's answer back out of it. The real sys.stdout also exposes a binary .buffer, and a StringIO does not, so a correct solution that writes with sys.stdout.buffer.write(...) raises AttributeError inside the sandbox and is graded as wrong.

Writing bytes straight to the buffer is an ordinary fast-output idiom in competitive programming, so the grader was scoring solutions on how they emit their answer rather than on the answer.

Before:

print                      -> '6'
sys.stdout.write           -> '6'
sys.stdout.buffer.write    -> AttributeError: '_io.StringIO' object has no attribute 'buffer'

Fix

The fake stdout now carries a .buffer that decodes writes into the text stream Capturing reads from, so buffered output lands in the captured result and keeps its order relative to print(). Undecodable bytes are replaced rather than raising, since a grader should not crash on a solution's output.

RawIOBase rather than BytesIO is deliberate, and it is the part worth reviewing. BytesIO implements writelines in C against its own internal buffer, so it bypasses an overridden write and the output is dropped with no error:

class WriteThrough(BytesIO):
    def __init__(self, text):
        super().__init__()
        self._text = text

    def write(self, data):
        self._text.write(bytes(data).decode())
        return len(data)

t = StringIO()
b = WriteThrough(t)
b.write(b"one\n")
b.writelines([b"two\n", b"three\n"])
print(repr(t.getvalue()))   # 'one\n'  <- two and three are gone

That would trade a loud AttributeError for a quiet wrong answer, which is the worse outcome for a grader. RawIOBase routes writelines through the overridden write.

Tests

tests/unit/tasks/test_lcb_capturing.py covers print(), sys.stdout.write, sys.stdout.writelines, and both buffer write paths. All of them print the same answer and all are required to capture identically. It also covers interleaving of text and binary writes, the byte count write returns, restoration of the real sys.stdout, and undecodable bytes.

The buffer cases fail on main with AttributeError and pass here.

Relationship to #1255 and #1257

This is the output-side counterpart of #1255, which reports the same defect on sys.stdin. That one is already being fixed in #1257, so I have deliberately left call_method untouched and the two do not overlap. #1257 changes call_method, this changes Capturing, and they add different test files.

Closes #1464