Memory exposure via uninitialized Read buffer

Use of uninitialized memory in buffoon 0.5.0 and earlier allows attackers to expose process memory or trigger undefined behavior. InputStream::read_exact creates an uninitialized buffer and passes it to a caller-supplied Read implementation, which can inspect prior memory contents or misreport the bytes written. Reachability depends on a consuming Rust application invoking this API with an arbitrary Read implementation; the resulting undefined behavior can expose memory or disrupt the process.