feat: look up last value of vault parameters when upgrading

[Chris-Hibbert]

closes: #10031

Description

Security Considerations

The values of the VaultManager parameters was lost on upgrade. They're recoverable, but I'll probably start from this code when upgrading other contracts.

Scaling Considerations

N/A

Documentation Considerations

N/A

Testing Considerations

Verifying my hypothesis in a3p tests.

Upgrade Considerations

yes

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[Chris-Hibbert]

The value retrieved for the vaultDirector's parameters is reasonable when I get a subscription, wrap it in a notifier, and call getUpdateSnce().

When I do the same with a subscription from a vaultManager for a particular brand, I get bizarre results.
for ATOM, I start with getUpdateSince(), and get DebtLimit: 0n InterestRate: 1%, LiquidationMargin: 1.5, LiquidationPadding: 25%, LiquidationPenalty: 1%, MintFee: .5%
I respond with getUpdateSince(1n), and get DebtLimit: 123_000_000_000_000n
After that, I call getUpdateSince() again, and get DebtLimit: 123_000_000_000_000n

With stATOM, I get DebtLimit: 1_000_000_000n on the first request.

The thing I don't understand is why getUpdateSince() would change its answer when there hasn't been any update to the stream of values.

These tests are in a3p.