chore: clean up L1 tests

[jackchuma]

Cleans up and simplifies the L1 test files for improved readability and maintainability.

• Promote ad-hoc test addresses and target balances to named constants for clarity
• Inline single-use locals (e.g. proxy/implementation handles) inside setUp
• Replace repeated vm.expectEmit(...) boilerplate with focused _expect* helpers
• Use locally-scoped arrays instead of mutating shared storage in negative-path tests
• Tighten assertions to reduce duplication while preserving coverage

[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