Add an option to create MemDB iterators with no Mutex for the CacheKVStore

[ValarDragon]

This is what we should be using in the SDK for the memDB CacheKVStore invocation there, to get the same guarantees around iterator closing as is present now. (Also this is just faster)

After this, I'll submit a PR that should significantly improve performance of Next operation. (Removes lots of channel overhead)

[codecov[bot]]

Codecov Report

Merging #187 (3f78a1d) into release/0.6.x (6f9a08c) will decrease coverage by 0.19%. The diff coverage is 50.00%.

@@                Coverage Diff                @@
##           release/0.6.x     #187      +/-   ##
=================================================
- Coverage          68.78%   68.58%   -0.20%     
=================================================
  Files                 27       27              
  Lines               1448     1458      +10     
=================================================
+ Hits                 996     1000       +4     
- Misses               377      383       +6     
  Partials              75       75              

Impacted Files	Coverage Δ
memdb.go	69.11% <0.00%> (-6.69%)	:arrow_down:
memdb_iterator.go	94.28% <100.00%> (+0.34%)	:arrow_up:

Impacted Files	Coverage Δ
memdb.go	69.11% <0.00%> (-6.69%)	:arrow_down:
memdb_iterator.go	94.28% <100.00%> (+0.34%)	:arrow_up:

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ValarDragon]

Can someone get the workflows to run plz?

[tac0turtle]

sorry, all looks goog