wand optimize cursor class

[zhengbuqian]

the main change is to update the cursor class to cache certain info, as per the perf result those size() calls used quite a lot of extra CPU cycles

also simplifed code to drop less important elements

simple benchmark result(time used to search all queries once on the full dataset) with drop ratio build 0.32 and drop ratio search 0.6:

	Before	After	Improvement %
bigann SPLADE vectors of MSMarco	141,473ms	89,604ms	36%
Milvus 2.5 Full Text Search Vectors of MSMarco(using IP/TF-IDF metric though, not BM25)	4,758ms	3,154ms	34%

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[mergify]

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1. If you're fixing a bug, label it as kind/bug.
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[zhengbuqian]

/kind improvement

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.37%. Comparing base (3c46f4c) to head (128cdb5).
Report is 260 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##           main     #968       +/-   ##
=========================================
+ Coverage      0   74.37%   +74.37%     
=========================================
  Files         0       82       +82     
  Lines         0     6685     +6685     
=========================================
+ Hits          0     4972     +4972     
- Misses        0     1713     +1713     

see 82 files with indirect coverage changes

[alexanderguzhva]

just double-checking that this is not total_num_vec_ - 1. According to standard naming conventions, id_ is assumed to be something within [0, num) range.

[zhengbuqian]

yes it is not total_num_vec_ - 1. When id_ is in [0, num) range it is still in range and the cursor is pointing at some doc, loc_ >= lut_size_ means it is out of range and the cursor points at no doc.

[alexanderguzhva]

/lgtm

[zhengbuqian]

issue: #967