Reduce allocations in Queue and Memory estimations

[benaadams]

Changes:

• Cache counts and reuse if ConcurrentDictionary not changed
• Reuse ConcurrentDictionary enumerator
• Iterate rather than using Linq when calculating

Removes the allocations from ShouldBuildANewBatch

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

• Yes
• No

[asdacap]

LGTM