Function decimal128_to_be16 

pub fn decimal128_to_be16(col: &Decimal128Array) -> BinaryArray

Encodes a Decimal128 column as fixed 16-byte big-endian two’s-complement binary.

Matches the wire format produced by evm-decode’s large_int_as_binary for int128 and uint128. Works for both signed and unsigned 128-bit integers (the byte pattern is identical).