test(storage): fix assert.throws and assert.rejects violations

[thiyaguk09]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request refactors several test files under handwritten/storage/test/ to improve type safety, fix incorrect assertion patterns, and clean up asynchronous code. Notably, it corrects broken assert.throws usages (which previously used comma expressions that did not actually validate the error message) by wrapping the expected error messages in new RegExp(...). It also replaces Promise.resolve().then(...) with process.nextTick(...) for asynchronous callbacks, adds missing await keywords to assert.rejects calls, and replaces any types with more specific types. The review feedback recommends further improving the assert.throws assertions by passing a validation object with a message property (e.g., { message: ... }) instead of using new RegExp(...), which is cleaner, avoids regex compilation overhead, and ensures a strict equality check.