Handle the raw payloads in requests and responses to convert-endpoint. This change replaces Base64-encoded I/O with direct binary streaming, yielding several benefits: - **Network efficiency**: Eliminates the ~33% size inflation of Base64, cutting bandwidth and latency. - **Memory savings**: Enables piping DOCX (already compressed) buffers straight to DocSpec API without holding, encoding and decoding multi-MB payload in RAM. Signed-off-by: Stephan Meijer <me@stephanmeijer.com>