refactor and test: adding check for service bonds

[kupermind]

• Adding check for service bonds;
• Adding a parameter for a minimum number of staking periods;
• Modifying tests.

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (6e825e2) 99.25% compared to head (aace8ba) 99.13%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
contracts/staking/ServiceStakingBase.sol	94.73%	1 Missing ⚠️
contracts/staking/ServiceStakingToken.sol	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #146      +/-   ##
==========================================
- Coverage   99.25%   99.13%   -0.12%     
==========================================
  Files          20       20              
  Lines        1606     1620      +14     
  Branches      296      300       +4     
==========================================
+ Hits         1594     1606      +12     
- Misses         12       14       +2     

Flag	Coverage Δ
unittests	99.13% <92.59%> (-0.12%)	⬇️

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