fix: more audit remediations

[shaspitz]

Describe your changes

More audit fixes! These ones don't necessarily correspond to findings from the official report, as some of them are low/info severity.

Changes:

• ValidatorOptInRouter.areValidatorsOptedIn now returns a struct containing three booleans representing which registries a validator is registered with. This will be useful for oracle slashing logic. Commit: 6d49ffd. This PR includes off-chain updates for this change in api.
• Setter for Gateway.relayer was added, along w/ missing tests for related setters. Commit: 530add7
• We now check the return value of IEnumerableSet.add in the middleware contract, and revert if the add fails. Note this revert shouldn't happen and would indicate state corruption. Commit: 9c39370
• Adds documentation on how the oracle should handle frozen validators registering with other registries. Commit: f9a200c
• Adds wouldVaultBeValidWith function to the middleware contract, along with documentation. The new function assists the owner account in confirming preconditions prior to calling setSlashPeriodSeconds. Commit: 4223760
• Updates our eigenlayer reference to their latest mainnet commit, and updates our mock implementations for their contracts. Commit: c7b4e87
• Updates symbiotic reference to their latest main commit, note they don't have a specified production version to reference yet. Commit: 5c71ece
• Removes any modifiers from MevCommitAVS that could possibly change in state during the underlying function call, following solidity best practice. Commit: e6155f4.
• Further simplify symbiotic veto slashing logic. This changes the symbiotic middleware slashing protocol such that the oracle calls requestSlash and executeSlash in the same tx. This builds off feat: streamlined symbiotic veto slasher handling #466. Commit: d1f7fdd.

Checklist before requesting a review

• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation