Update the src/test/token/TokenERC20.t.sol

[ianpurifying]

Add Tests for Signature Validation and Gas Efficiency

I added the testFailMintWithInvalidSignature to check if minting with an invalid signature fails as expected. Introduced testGasMinting to log gas usage during the minting process for efficiency tracking. Aligned MintRequest structure in tests with existing contract setup.

Reason: Strengthens security by ensuring only valid signatures can mint tokens. Provides insights into gas costs for minting operations.

Impact: No breaking changes; purely additive tests for better coverage.