rust-filepatterns: unescape comment character property There were multiple issues in the original implementation: a. the local variable "line" dropped soon after replace_slice() applied b. replace_slice() was noop since br"\#".len() != b"#" This patch uses bytes::Regex::replace_all() since it seems the simplest way to replace bytes of arbitrary length, and I don't think we have to avoid using Regexp here.

rust-filepatterns: use literal b'#' instead of cast

rust-filepatterns: fix type of warnings tuple to (bytes, bytes) Otherwise warn() in match.py would fail if the warning contains non-ASCII character. We might want to add a thin ByteString wrapper around Vec<u8> to implement ToPyObject<ObjectType = PyBytes>, but I'm not sure.