Function parseSchema

Parse an Arrow schema from IPC format bytes

The schema bytes format from Flight:

• 4 bytes: IPC_CONTINUATION_TOKEN (0xFFFFFFFF)
• 4 bytes: message length
• flatbuffer Message with Schema header

Uses MessageReader to parse schema-only IPC messages, which is the correct approach for FlightInfo.schema bytes (as opposed to RecordBatchReader which expects a full IPC stream with record batches).