support int128 uint128 with gcc or clang

[982945902]

Why

complete potion TODO

What is changing

support int128 uint128 with gcc or clang

Example

TEST_CASE("int128/uint128") {
using int128_t = __int128;
using uint128_t = signed __int128;

{
int128_t it = -2131231231213123;

auto ts = struct_pack::serialize(it);

auto it_ = struct_pack::deserialize<int128_t>(ts);

CHECK(it == it_);
}

{
uint128_t it = 2131231231213123;

auto ts = struct_pack::serialize(it);

auto it_ = struct_pack::deserialize<uint128_t>(ts);

CHECK(it == it_);
}

}

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Thanks you!

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I will add document & testcase later.