This PR contains improvements related to usage of std::vector and looping over containers in the range-for loop.
It is advised to use `std::vector::reserve()` to avoid unneeded memory allocations when the total size is known beforehand.
When looping over a container that stores non-trivial types usage of const reference is advised to avoid redundant copies.
Closesscylladb/scylladb#16978
* github.com:scylladb/scylladb:
api/api.hh: use const reference when looping over container
api/api.hh: use std::vector::reserve() when the total size is known
b341aa8f6d