Add io.BytesIO.peek() method to read without advancing position.
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com> Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com> Co-authored-by: Victor Stinner <vstinner@python.org> Co-authored-by: Emma Smith <emma@emmatyping.dev> Co-authored-by: Stan Ulbrych <stan@python.org> Co-authored-by: Cody Maloney <cmaloney@users.noreply.github.com>