Split up base account to fit under size limit

[adam-alchemy]

Motivation

The contract size of UpgradeableModularAccount exceeds the 24.5kb size limit. While the intention behind the reference implementation is not that it should be used in production, this makes it difficult to test integrations with outside of the context of foundry tests and other forked environments.

Solution

Split out PluginManagerInternals into a distinct PluginManager contract. UpgradeableModularAccount performs delegatecalls into this contract, much like a library. However, using a delegate-only contract over a library gives us easier integration into deployment tools like scripts.

This brings the size for both contracts under the limit.

Also fixes a compiler warning and removes the ignored error codes.

[fangting-alchemy]

lgtm, thanks.

[huaweigu]

What're the tradeoffs between this approach vs library external function?

[adam-alchemy]

Using a library with external functions is a bit less straightforward to deploy through foundry. This pattern of manually delegatecalling a custom contract also lets us inspect calls between the account and the plugin manager implementation better, because we know the abi-encoding format. Libraries would use the solidity-internal custom encoding for libraries: https://docs.soliditylang.org/en/v0.8.19/contracts.html#function-signatures-and-selectors-in-libraries

Also, as a note for the future: this change is intended to make it easier to work with the reference implementation as of the current version: Spec Update 6, aka v0.6.0. We hope to remove this workaround as the standard gets simplified in the future version v0.7.0 and have a single-contract reference implementation, even without optimizations.