Use last epoch hotkey alpha for fee calculation

[gztensor]

Description

• Use last epoch total hotkey alpha in staking fee calculation so that sharp changes in total hotkey alpha don't affect fees.
• Also add TotalHotkeyAlphaLastEpoch, AlphaDividendsPerSubnet, and TaoDividendsPerSubnet to swap_hotkey.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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[camfairchild]

Needs tests:

• unstaking with no prev epoch stake
• unstaking with lower prev epoch stake than current stake