This is a code simplification and an optimization when serializing (pre)vectors of `std::byte` and `int8_t`
> refactor: use "if constexpr" in (pre)vector's (Un)Serialize()
>
> This gets rid of unnecessarily creating a temporary object T() to call the right function.
https://github.com/bitcoin/bitcoin/pull/28203/commits/c8839ec5cd81ba9ae88081747c49ecc758973dd1
https://github.com/bitcoin/bitcoin/pull/28203/commits/0fafaca4d3bbf0c0b5bfe1ec617ab15252ea51e6
https://github.com/bitcoin/bitcoin/pull/28203/commits/088caa68fb8efd8624709d643913b8a7e1218f8a
https://github.com/bitcoin/bitcoin/pull/28203/commits/f054bd072afb72d8dae7adc521ce15c13b236700
> Faster std::byte (pre)vector (un)serialize
https://github.com/bitcoin/bitcoin/pull/29114/commits/facaa14785e006c1af5a8b17b10e2722af8d054e
> Allow int8_t optimized vector serialization
>
> int8_t serialization is allowed, but not the optimized vector
> serialization. Fix that.
https://github.com/bitcoin/bitcoin/pull/29114/commits/fab41697a5448ef2861f65795bd63a4ccdda6a40
This concludes backport of core#28203 and core#29114