storage_proxy uses std::vector<inet_address> for small lists of nodes - for replication (often 2-3 replicas per operation) and for pending operations (usually 0-1). These vectors require an allocation, sometimes more than one if reserve() is not used correctly.
This series switches storage_proxy to use utils::small_vector instead, removing the allocations in the common case.
Test results (perf_simple_query --smp 1 --task-quota-ms 10):
```
before: median 184810.98 tps ( 91.1 allocs/op, 20.1 tasks/op, 54564 insns/op)
after: median 192125.99 tps ( 87.1 allocs/op, 20.1 tasks/op, 53673 insns/op)
```
4 allocations and ~900 instructions are removed (the tps figure is also improved, but it is less reliable due to cpu frequency changes).
The type change is unfortunately not contained in storage_proxy - the abstraction leaks to providers of replica sets and topology change vectors. This is sad but IMO the benefits make it worthwhile.
I expect more such changes can be applied in storage_proxy, specifically std::unordered_set<gms::inet_address> and vectors of response handles.
Closes#8592
* github.com:scylladb/scylla:
storage_proxy, treewide: use utils::small_vector inet_address_vector:s
storage_proxy, treewide: introduce names for vectors of inet_address
utils: small_vector: add print operator for std::ostream
hints: messages.hh: add missing #include
abe3d7d7d3