Added an Aave integration

[jalextowle]

Resolved Issues

Description

Implemented an AaveHyperdrive instance. Due to the higher-than-usual complexity of this integration, code size became a limitation. To side-step this issue, a fourth target was added to the deployment.

The most interesting part of this integration is that Aave has an internal shares mechanism but doesn't expose very many details about it. For example, Aave doesn't have functions like sharesOf, convertToShares, or convertToBase. It also uses 27 digit fixed point precision when performing conversions from shares to base or from base to shares. This led to the integration looking more similar to the EzETH integration than it does to the StETH integration. The share conversion logic should be reviewed closely.

Review Checklists

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[[Reviewer Name]]

• Tokens
  • Do all approve calls use forceApprove?
  • Do all transfer calls use safeTransfer?
  • Do all transferFrom calls use msg.sender as the from address?
    • If not, is the function access restricted to prevent unauthorized
      token spend?
• Low-level calls (call, delegatecall, staticcall, transfer, send)
  • Is the returned success boolean checked to handle failed calls?
  • If using delegatecall, are there strict access controls on the
    addresses that can be called? It shouldn't be possible to delegatecall
    arbitrary addresses, so the list of possible targets should either be
    immutable or tightly controlled by an admin.
• Reentrancy
  • Are functions that make external calls or transfer ether marked as nonReentrant?
    • If not, is there documentation that explains why reentrancy is
      not a concern or how it's mitigated?
• Gas Optimizations
  • Is the logic as simple as possible?
  • Are the storage values that are used repeatedly cached in stack or
    memory variables?
  • If loops are used, are there guards in place to avoid out-of-gas
    issues?
• Visibility
  • Are all payable functions restricted to avoid stuck ether?
• Math
  • Is all of the arithmetic checked or guarded by if-statements that will
    catch underflows?
  • If Safe functions are altered, are potential underflows and
    overflows caught so that a failure flag can be thrown?
  • Are all of the rounding directions clearly documented?
• Testing
  • Are there new or updated unit or integration tests?
  • Do the tests cover the happy paths?
  • Do the tests cover the unhappy paths?
  • Are there an adequate number of fuzz tests to ensure that we are
    covering the full input space?

[jrhea]

I just have a few nits, but I am going to go ahead and approve.