Determine what memory allocator to use at runtime

When trying to build magma as a shared library we ran into issues because jemalloc was set to be used however the memory was actually allocated using malloc. So when methods from `ArenaMalloc` were used they used jemalloc but the memory belonged to malloc. (for more info see this thread: https://couchbase.slack.com/archives/CDNGWKZ7D/p1696346362078789)

We need to check what allocator we are using at runtime and decide whether we should use the `ArenaMalloc` methods or the general malloc methods.