Skaled 1674 kill snapsot sending monitoring thread

[dimalit]

if skaled is sending snapshot, and is asked to exit - it should kill threads that monitor snapshot sending timeouts
Fixes #1674

[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

Merging #1676 (3d5f19b) into develop (28a3458) will increase coverage by 0.00%.
Report is 1 commits behind head on develop.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1676   +/-   ##
========================================
  Coverage    44.96%   44.96%           
========================================
  Files          347      347           
  Lines        51283    51283           
========================================
+ Hits         23058    23059    +1     
+ Misses       28225    28224    -1