Rewrite & optimize LimitedQueue (#3798)

* Use circular buffer for LimitedQueue

* Reduce copying of snapshot

* Small optimizations

* Remove unneeded lock statements

* Add LimitedQueue tests

* Fix includes for limited queue benchmark

* Update CHANGELOG.md

* Use correct boost version iterators

* Use a shared_mutex to clarify reads and writes

* Update `find`/`rfind` to return the result as a boost::optional

* Use `[[nodiscard]]` where applicable

* Update comments

* Add a couple more doc comments

* Replace size with get

get is a safe (locked & checked) version of at

* Use std::vector in LimitedQueueSnapshot

* Update LimitedQueue benchmarks

* Add mutex guard to buffer accessors

We do not know whether T is an atomic type or not
so we can't safely say that we can copy the value
at a certain address of the buffer.

See https://stackoverflow.com/a/2252478

* Update doc comments, add first/last getters

* Make limit_ const

* Omit `else` if the if-case always returns

* Title case category comments

* Remove `at`

* Fix `get` comment

* Privatize/comment/lock property accessors

 - `limit` is now private
 - `space` is now private
 - `full` has been removed
 - `empty` now locks

* Remove `front` function

* Remove `back` method

* Add comment to `first`

* Add comment to `last`

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/Scrollbar.cpp

@@ -32,8 +32,7 @@ Scrollbar::Scrollbar(ChannelView *parent)
 
 void Scrollbar::addHighlight(ScrollbarHighlight highlight)
 {
-    ScrollbarHighlight deleted;
-    this->highlights_.pushBack(highlight, deleted);
+    this->highlights_.pushBack(highlight);
 }
 
 void Scrollbar::addHighlightsAtStart(
@@ -62,7 +61,7 @@ void Scrollbar::clearHighlights()
     this->highlights_.clear();
 }
 
-LimitedQueueSnapshot<ScrollbarHighlight> Scrollbar::getHighlightSnapshot()
+LimitedQueueSnapshot<ScrollbarHighlight> &Scrollbar::getHighlightSnapshot()
 {
     if (!this->highlightsPaused_)
     {
@@ -275,7 +274,7 @@ void Scrollbar::paintEvent(QPaintEvent *)
     }
 
     // draw highlights
-    auto snapshot = this->getHighlightSnapshot();
+    auto &snapshot = this->getHighlightSnapshot();
     size_t snapshotLength = snapshot.size();
 
     if (snapshotLength == 0)