[RFC] feat: seek return Ordering for binary search

[MrCroxx]

Make seek return an Ordering for binary search on iterators. With it, we can use a binary_search_by(Future<Output=Ordering>) pattern for binary search seek.

Note: There is no built-in async binary search support. IMO, seek on Seek::Random is just I want to perform binary search seek, but the existing interfaces seems enough. Not sure if this is necessary.

    /// `seek` returns [`Ordering`] for binary search, which incidates the comparison between
    /// expection key and result key. Seeking for first or last postion always returns
    /// `Ordering::Equal` .

[MrCroxx]

Codecov Report

Merging #11 (85e0646) into main (560810a) will decrease coverage by 0.08%. The diff coverage is 95.00%.

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   93.84%   93.76%   -0.09%     
==========================================
  Files          12       12              
  Lines         569      577       +8     
==========================================
+ Hits          534      541       +7     
- Misses         35       36       +1     

Impacted Files	Coverage Δ
storage/src/iterator/block_iterator.rs	98.26% <88.88%> (-0.55%)	:arrow_down:
storage/src/iterator/concat_iterator.rs	98.47% <100.00%> (+0.03%)	:arrow_up:

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[MrCroxx]

Duplicated with #14 , close.