Use buffered iterators to speed up the search

Nobody has claimed this yet.

Currently, `op_iter` functions use `Vec` to collect `op` results to `vec` and returns `vec.into_iter()`.
I recommend use buffered lock-free iterator generator crate - [`buter`](https://crates.io/crates/buter) or similar

For example, it will look like this:
```rust
//! before
let mut vec = Vec::with_capacity(...);
self.each(..., |link| {
vec.push(link);
Continue
});
vec.into_iter()

//! after
let writer = self.buter.writer();
self.each(..., |link| {
writer.extend(Some(link));
Continue
});
writer.into_iter()
```

Locate the `op_iter` functions and inspect how they collect `op` results into a `Vec` before returning `into_iter()`. Compare the proposed `buter` or similar buffered iterator approach across the affected search paths; done means the relevant iterators no longer use the current collection pattern and the search is measurably faster.

Written by the indexing model from the issue text.