Snowflake data type wrong mapping for decimal

The mapping for decimal data type should be "real" instead of "numeric"

https://github.com/sqlpipe/sqlpipe/blob/a589ca07ab53f3d88be0eb3a369c20fad09ba6b2/cmd/sqlpipe/system_snowflake.go#L145C1-L146C23

`	case "decimal":
		return "number", nil
`

A decimal number with decimal digits will be truncated with the current mapping in place.
