PE-7351: correctly account for moving stakes during redelegation

[arielmelendez]

Issues found:

• LastKnownWithdrawSupply being ADDED to rather than subtracted from
• LastKnownStakedSupply not being added to in the case where a delegation withdraw vault is used to redelegate to a new gateway
• (minor) incorrect types returned from gar.redelegateStake

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.44%. Comparing base (7edaece) to head (e191e23).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #299   +/-   ##
========================================
  Coverage    94.44%   94.44%           
========================================
  Files           10       10           
  Lines         2990     2990           
========================================
  Hits          2824     2824           
  Misses         166      166           

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