chore(tests): simplify universal tests

[jackchuma]

What changed? Why?

Simplifies the universal test suite by removing repeated setup, repeated assertions, and duplicate getter/interface coverage across the affected tests.

This keeps the same behavioral coverage while making the tests shorter and easier to review. The cleanup touches the universal test files for CrossDomainMessenger, multisig scripts, OptimismMintableERC20, Proxy, ProxyAdmin, ProxyAdminOwnedBase, StandardBridge, WETH98, and related helpers.

Notes to reviewers

• This is test-only and does not change production contracts.
• Proxy tests now deploy Proxy directly instead of going through DeployUtils.create1.
• CrossDomainMessenger tests now use ForgeArtifacts.getSlot to look up the portal l2Sender storage slot instead of relying on a hardcoded slot index.
• Several tests now share small helper functions for repeated minting, proxy admin calls, gas calculations, and message status assertions.

How has it been tested?

• FOUNDRY_PROFILE=lite forge test --match-path 'test/universal/*.t.sol'

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1