Optimize formatTime utility (#3777)

Adds benchmarks and unit tests for the function

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

benchmarks/CMakeLists.txt

@@ -3,6 +3,7 @@ project(chatterino-benchmark)
 set(benchmark_SOURCES
     ${CMAKE_CURRENT_LIST_DIR}/src/main.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/Emojis.cpp
+    ${CMAKE_CURRENT_LIST_DIR}/src/FormatTime.cpp
     # Add your new file above this line!
     )