perf(library/shared_environment): replace shared_mutex with simple mutex, the shared_mutex is just overhead and impacts negatively on performance tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(build): add GPROF compilation mode for using gprof

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): move slow tests to tests/lua/slow

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(*): tag 'slow' tests as 'expensive', and exclude 'expensive' tests when testing under valgrind

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>