bug(vesting): clawback only unvested coins

[danburck]

Description

This PR adds integration tests for clawback, remove unnecessary staking logic during clawback (as staking unvested tokens is not allowed ) and refactors the clawback to only allow clawback of unvested tokens.

[codecov]

Codecov Report

Merging #317 (bda2642) into main (b71526c) will increase coverage by 0.49%.
The diff coverage is 100.00%.

❗ Current head bda2642 differs from pull request most recent head a9b9823. Consider uploading reports for the commit a9b9823 to get more accurate results

@@            Coverage Diff             @@
##             main     #317      +/-   ##
==========================================
+ Coverage   65.04%   65.53%   +0.49%     
==========================================
  Files          93       93              
  Lines        6191     6137      -54     
==========================================
- Hits         4027     4022       -5     
+ Misses       2007     1963      -44     
+ Partials      157      152       -5     

Impacted Files	Coverage Δ
x/vesting/keeper/msg_server.go	88.95% <100.00%> (+13.39%)	⬆️
x/vesting/types/clawback_vesting_account.go	96.42% <100.00%> (+7.62%)	⬆️
x/vesting/types/schedule.go	100.00% <100.00%> (ø)
x/vesting/types/utils.go	100.00% <0.00%> (+8.82%)	⬆️

[fedekunze]

ACK, pending changelog entry