Overwrite balance to account for debt in strategies

[MickdeGraaf]

User Story

• As an <audience/user>: User/Integrator
• I want to <action/task>: The pievault to take into account debt in strategies
• so that <outcome/goal/benefit>: Entry and exit properly accounts for balances in strategies

Type

• Enhancement
• Maintenance
• Refactor

Description

Needed to be able to support Yearn strategies.

Definition of Done

• Overwrite balance to account for debt in strategies
• Unit test above

Part of #30
Partly implemented in yearn-strategy-support