chore(kernel/replace_fn): "name" constant
perf(kernel/expr_eq_fn): use thread local cache, and avoid memory allocation/deallocation
perf(kernel/metavar): used thread local cache for instantiate_metavars
perf(util/list): use memory pool for list cells
fix(kernel/metavar): compilation error in some compilers
fix(kernel/metavar): compilation error in some compilers