CollectionIterator improvements

[viceroypenguin]

This PR updates a couple missed optimizations in the existing CollectionIterator improvements:

• Update a couple missed sealed classes
• Take advantage of TryGetCollectionCount() on certain iterators that don't use CopyTo, that is, they only implement ICollection<> for the .Count optimizations

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.09 ⚠️

Comparison is base (ea91311) 87.90% compared to head (6b318e2) 87.82%.

❗ Current head 6b318e2 differs from pull request most recent head 1dabdf2. Consider uploading reports for the commit 1dabdf2 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #409      +/-   ##
==========================================
- Coverage   87.90%   87.82%   -0.09%     
==========================================
  Files         239      238       -1     
  Lines        7452     7393      -59     
  Branches     1719     1704      -15     
==========================================
- Hits         6551     6493      -58     
- Misses        461      462       +1     
+ Partials      440      438       -2     

Impacted Files	Coverage Δ
Source/SuperLinq/PreScan.cs	100.00% <ø> (ø)
Source/SuperLinq/Scan.cs	100.00% <ø> (ø)
Source/SuperLinq/ScanRight.cs	100.00% <ø> (ø)
Source/SuperLinq/Do.cs	100.00% <100.00%> (+2.32%)	⬆️
Source/SuperLinq/Rank.cs	100.00% <100.00%> (ø)
Source/SuperLinq/ScanBy.cs	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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