gh-141968: Use take_bytes to simplify and remove copy from pyrepl BaseEventQueue

[lgeiger]

This PR uses bytearray.take_bytes to simplify pyrepl's BaseEventQueue.flush_buf and remove copies from BaseEventQueue.push

import timeit
from statistics import mean, stdev

times = timeit.repeat(
    "[q.push(b) for b in data]",
    setup=(
        "from _pyrepl.base_eventqueue import BaseEventQueue\n"
        "q = BaseEventQueue('utf-8', {})\n"
        "data = b'hello world' * 8\n"
    ),
    number=50_000,
    repeat=5,
)
print(f"{mean(times) * 1e3:.2f} ± {stdev(times) * 1e3:.2f} ms")

main:    1845.39 ± 10.02 ms
this PR: 1371.56 ± 3.85 ms

• Issue: Remove bytearray to bytes copies in stdlib using take_bytes #141968

[maurycy]

cc @cmaloney

[maurycy]

Maybe this method is redundant now?

[lgeiger]

I'm happy to remove the function. For now I kept it to keep the diff small. But happy to remove it and just use self.buf.take_bytes() instead. Let me know what you prefer.