chore(tests): simplify util and vendor tests

[jackchuma]

What changed? Why?

Simplifies the utility and vendor test suites by reducing repeated test setup and reusing common calldata construction.

• Adds helper constructors for repeated CBMulticall call payloads and makes delegatecall failures bubble the underlying revert data in the test helper.
• Reuses initializer calldata across implementation/proxy pairs in Initializable.t.sol and removes the unused nickname indirection.
• Updates the OpenZeppelin v5 initializer test to import the v5 Initializable type directly, reuse FeeVault constructor/init calldata, and assert the expected custom error selector.
• Removes redundant test comments where the test name already captures the behavior.

Notes to reviewers

This is intended to be a test-only cleanup. The production contract surface is unchanged.

The CBMulticallDelegateCaller test helper now bubbles revert data so the non-allowed delegatecall failure test can assert the expected "Multicall3: call failed" revert instead of accepting any revert.

How has it been tested?

forge test --match-path test/utils/CBMulticall.t.sol

Result: 26 passed, 0 failed, 0 skipped.

[cb-heimdall]

✅ Heimdall Review Status

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