Meta-issue for performance improvements found by Clang-Tidy

[KvanTTT]

• performance-inefficient-vector-operation
  • emplace_back -> push_back on corresponding call sites. It looks trivial and safe.
  • Use reserve to avoid unnecessary memory reallocations. It's also quite straightforward.
• performance-unnecessary-copy-initialization
  • Preliminary: readability-non-const-parameter
  • Preliminary: readability-make-member-function-const
  • Main step. I've found a lot of places with redundant copying, it could improve performance.