Fix Concurrent Use of KV Iterators

[alexanderkiel]

The cost of opening an iterator doesn't impact the query performance in a significant way. Especially if we have a CQL Cache through #1051 the performance impact would be negligible.

I didn't make this as bug because the problem was only exposed by #1244 which was not released before.

Closes: #1217

[codecov]

Codecov Report

Merging #1262 (ae85e62) into develop (a916cf4) will decrease coverage by 0.01%.
Report is 1 commits behind head on develop.
The diff coverage is 97.80%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1262      +/-   ##
===========================================
- Coverage    95.26%   95.25%   -0.01%     
===========================================
  Files          242      242              
  Lines        15342    15394      +52     
  Branches       355      357       +2     
===========================================
+ Hits         14616    14664      +48     
- Misses         371      373       +2     
- Partials       355      357       +2     

Files	Coverage Δ
modules/db/src/blaze/db/impl/db.clj	97.18% <100.00%> (ø)
modules/db/src/blaze/db/impl/index.clj	100.00% <100.00%> (ø)
...b/src/blaze/db/impl/index/compartment/resource.clj	98.18% <100.00%> (+0.10%)	⬆️
...ules/db/src/blaze/db/impl/index/resource_as_of.clj	98.43% <100.00%> (+0.18%)	⬆️
...laze/db/impl/index/resource_search_param_value.clj	100.00% <100.00%> (ø)
...odules/db/src/blaze/db/impl/index/system_as_of.clj	100.00% <100.00%> (ø)
modules/db/src/blaze/db/impl/index/type_as_of.clj	100.00% <100.00%> (ø)
modules/db/src/blaze/db/impl/search_param.clj	100.00% <ø> (ø)
...ules/db/src/blaze/db/impl/search_param/chained.clj	100.00% <100.00%> (ø)
.../db/impl/search_param/composite/token_quantity.clj	97.14% <100.00%> (ø)
... and 10 more