test: add ERC-20 storage utils for state setup

[lumoswiz]

Summary

• Introduced a storage utility for ERC-20 tests so we can set balances, allowances, and total supply directly, reducing reliance on bloated harnesses when facets expose only partial functionality.

Changes Made

• Added ERC20StorageUtils under test/utils/storage/ with getters/setters and a mint helper that write directly to ERC-20 transfer storage slots.

Checklist

Before submitting this PR, please ensure:

• Code follows the Solidity feature ban - No inheritance, constructors, modifiers, public/private variables, external library functions, using for directives, or selfdestruct

• Code follows Design Principles - Readable, uses diamond storage, favors composition over inheritance

• Code matches the codebase style - Consistent formatting, documentation, and patterns (e.g. ERC20Facet.sol)

• Code is formatted with forge fmt

• Existing tests pass - Run tests to be sure existing tests pass.

• New tests are optional - If you don't provide tests for new functionality or changes then please create a new issue so this can be assigned to someone.

• All tests pass - Run forge test and ensure everything works

• Documentation updated - If applicable, update relevant documentation

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[github-actions]

Coverage Report

Metric	Coverage	Details
Lines	70%	1121/1601 lines
Functions	81%	283/348 functions
Branches	51%	114/224 branches

Last updated: Tue, 06 Jan 2026 17:10:33 GMT for commit e3f1918

[github-actions]

Gas Report

No gas usage changes detected between main and test/add-erc20-storage-utils.

All functions maintain the same gas costs. ✅

Last updated: Tue, 06 Jan 2026 17:10:54 GMT for commit e3f1918