Update ferret_cot.hpp

[kov072299]

• currently, FerretCOT's party is int type.
• code in write_pre_data128_to_file writes it as int64_t width.
• code in read_pre_data128_from_file reads int64_t into an int as well.

if sizeof(int64_t) != sizeof(int), stack clobbering in read, and out-of-bounds access in write.

proposed code is temporary fix, maintainers should replace with preferred fix.

[kov072299]

looks like this is partial duplicate of #92

[kov072299]

this issue is also explained in #89

[wangxiao1254]

I slightly modified the fix by enforcing that we always write 8 bytes to an 8-byte structure. I will merge it in a few days, in case anyone finds something wrong :)