* Remove unused namespace alias.
* Remove unused 'using' statements.
* Remove more unused 'using' and namspace aliases.
* Prefer absl::StrContains over comparing `find` result with `npos`.
* Remove more unused things.
* Prefer usage of `empty()` over `size()` when possible.
* Remove more unused things.
* Address code review.
* Address code review.
* More fixes to query_core.cc
* comment should match parameter name.
* Pre-allocate container capacity for better performance.
* More fixes.
* Fix inconsistent declaration parameter name.
* Fix inconsistent declaration parameter name.
* Fix inconsistent declaration parameter name.
* Address bugprone-inaccurate-erase (inappropriate `erase` overload was used).
* Fix return type of move and copy constructor.
* Fix bugprone use after move.
* Fix formatting.
* Reflect the param name change in the doc.