Doing a bunch of stuff with the unsafe package doesn't make much sense, we can just copy the implementation from the binary package. We can call the package lendian for now, put it under internal, and use it across the bson, builder, and elements packages. For now implement Uint32, Uint64, Int32, Int64, Decimal128, PutUint32, PutUint64, PutInt32, PutInt64, and PutDecimal128. All implementations should be little endian.

After the implementation is complete and tested, switch out the usage across the packages that aren't currently being worked on.