perf(kernel/type_checker): reduce the overhead of creating delayed_justification objects, a huge number of them is created when type checking applications

We reduce the cost by avoiding the allocation of std::functional objects, and the unnecessary increment/decrement of reference counters.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
perf(kernel/type_checker): reduce the overhead of creating delayed_justification objects, a huge number of them is created when type checking applications