'immutable' greatly reduces gas costs

[code423n4]

Handle

pauliax

Vulnerability details

Impact

There are variables that do not change so they can be marked as immutable to greatly improve the gas costs. Examples of such variables are:
contract ATokenYieldSource aToken, lendingPoolAddressesProviderRegistry.
contract IdleYieldSource idleToken, underlyingAsset.
contract YearnV2YieldSource vault, token.
contract ControlledToken controller.

Recommended Mitigation Steps

Mark such variables with the 'immutable' keyword.

[asselstine]

See #7

[dmvt]

duplicate of #7

[dmvt]

Consolidating around the non-critical risk level in deference to the sponsor's choice.