Rollup merge of #106692 - eggyal:mv-binary_heap.rs-binary_heap/mod.rs, r=Mark-Simulacrum

mv binary_heap.rs binary_heap/mod.rs

I confess this request is somewhat selfish, as it's made in order to ease synchronisation with my [copse](https://crates.io/crates/copse) crate (see eggyal/copse#6 for explanation). I wholly understand that such grounds may be insufficient to justify merging this request—but no harm in asking, right?