Bug/1588 change snapshot hash computation

[olehnikolaiev]

fixes #1588

do not force leveldb to store all the key-value pairs in OS buffer
instead iterate over the database batch by batch to decrease RAM usage during snapshot hash calculation

tested on devnet:

• update one node to the version with fix
• run load tests for the long time. you will see that RAM and swap usage is less for the updated node ( @oleksandrSydorenkoJ )
• non updated nodes will eventually fail with out of memory error, while updated node will stay healthy

[github-actions]

SUGGESTIONS BEFORE MERGE:

1. Build custom container here: https://github.com/skalenetwork/skaled/actions?query=workflow%3A%22Custom+Docker+and+Binary%22
2. Test it here: https://github.com/skalenetwork/skale-ci-integration_tests/actions?query=workflow%3A%22Skaled+Nightly+Tests%22
3. Edit VERSION file appropriately to your changes!
   See https://skalelabs.atlassian.net/wiki/spaces/SKALE/pages/2444951553/Branching+instructions

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (678f59b) 46.02% compared to head (a79c45d) 45.68%.

Additional details and impacted files

@@             Coverage Diff             @@
##           v3.18.0    #1787      +/-   ##
===========================================
- Coverage    46.02%   45.68%   -0.35%     
===========================================
  Files          358      358              
  Lines        51820    51878      +58     
===========================================
- Hits         23852    23701     -151     
- Misses       27968    28177     +209