self->hash API: inline, not indirect calls

mandate `T_hash` to be defined, resp. `TK_hash`, beforehand. Don't call it indirectly.
There's no need to dynamically change it, it needs to be compile-time.
Similarily for the same for the equal and compare funcs.
No need from them to be stored in the container. Inline them.
hash is esp. performance sensitive, but also security. just NULL it to create a DDOS.
