Add unbounded_queue_max_capacity to FrontEndOptions #161

Job	Run time
build (g++-8, Release, 17, ubuntu-22.04, ON)	9m 52s
build (g++-8, Debug, 17, ubuntu-22.04, ON)	7m 30s
build (g++-10, Debug, 17, ubuntu-22.04, ON)	7m 7s
build (g++-10, Release, 20, ubuntu-22.04, ON, -DQUILL_USE_VALGRIND=ON, -T memcheck, sudo apt -o A...	26m 37s
build (g++-10, Release, 17, ubuntu-22.04, OFF, -DQUILL_NO_EXCEPTIONS=ON)	2m 7s
build (g++-13, Release, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	12m 59s
build (g++-13, Debug, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	9m 6s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_ADDRESS=ON)	25m 21s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_THREAD=ON)	18m 1s
build (clang++-19, Release, 17, ubuntu-22.04, ON, wget -O - https://apt.llvm.org/llvm-snapshot.gp...	11m 54s
build (g++-10, Release, 17, ubuntu-22.04, ON)	10m 43s
	2h 21m 17s

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