Migrate KvIterator from Protocol to Interface

[alexanderkiel]

Protocol dispatch isn't as fast as interface dispatch and primitive types are not possible on protocols.

[codecov]

Codecov Report

Merging #676 (dca4e44) into develop (11e66b2) will decrease coverage by 0.09%.
The diff coverage is 67.64%.

@@             Coverage Diff             @@
##           develop     #676      +/-   ##
===========================================
- Coverage    93.60%   93.51%   -0.10%     
===========================================
  Files          235      235              
  Lines        13921    13918       -3     
  Branches       345      349       +4     
===========================================
- Hits         13031    13015      -16     
- Misses         545      554       +9     
- Partials       345      349       +4     

Impacted Files	Coverage Δ
modules/kv/src/blaze/db/kv.clj	82.35% <35.71%> (-17.65%)	⬇️
modules/db/src/blaze/db/impl/iterators.clj	94.28% <83.33%> (-5.72%)	⬇️
...ules/db/src/blaze/db/impl/index/resource_as_of.clj	97.63% <100.00%> (ø)
modules/kv/src/blaze/db/kv/mem.clj	100.00% <100.00%> (ø)
modules/rocksdb/src/blaze/db/kv/rocksdb.clj	99.04% <100.00%> (ø)