Make clippy (mostly) happy

[virtualritz]

These are almost entirely automatic fixes that cargo clippy --fix yielded.

As a result of those the next clippy run indentified some superfluous lifetimes that I removed.

Left is SeachResult::len(). This popped up because SearchResult misses is_empty(), the companion of len() that clippy laments should always be implemented. 😁

However, a Rust user would be suprised that len() returns Option<usize> and not usize.

I see two possibilities:

• Rename SearchResult::len() to try_len() to make it obvious that this returns an Option (or could even be Result and return the original Err) and keep the signature.

• Make it return an usize, i.e. map a possible encountered Err/None inside the function to the 0usize return value.

  In this case also add:

  fn is_empty(&self) -> bool {
      0 == self.len()
  }

[virtualritz]

Ah yeah, this is based on my previous PR which you can ignore if you merge this.