warnings during build

[Jean-Luc-Picard-2021]

Building Scryer Prolog with:

$ cargo build --release

Recently shows warnings:

warning: struct `OrderedOpDirKey` is never constructed
warning: method `unify_big_num` is never used
warning: ambiguous wide pointer comparison, the comparison includes metadata which may not be expected
warning: ambiguous wide pointer comparison, the comparison includes metadata which may not be expected

Anything to worry about?

[aarroyoc]

It seems that the Rust compiler got better at detecting these things. But they were already there, so I won't worry too much