Get MagicSpend test coverage to 100%

[stevieraykatz]

This PR implements a number of new tests for Magic Spend and also integrates with Coveralls CI to add automated coverage reporting and checking.

Added the following tests to improve our coverage reporting up to 100%:

1. Added missing unit tests for the ownerWithdraw() method
2. Added missing unit tests for the getHash() method
3. Added missing unit tests for the isValidWithdrawalSignature() method
4. Added a test case to ValidatePaymasterUserOp for revert case InsufficientBalance

As of this PR, coverage reported by forge coverage shows:

| File                             | % Lines         | % Statements    | % Branches      | % Funcs         |
|----------------------------------|-----------------|-----------------|-----------------|-----------------|
| script/DeployMagicSpend.s.sol    | 0.00% (0/8)     | 0.00% (0/10)    | 100.00% (0/0)   | 0.00% (0/2)     |
| src/MagicSpend.sol               | 100.00% (46/46) | 100.00% (54/54) | 100.00% (20/20) | 100.00% (16/16) |
| test/MagicSpend.t.sol            | 0.00% (0/6)     | 0.00% (0/10)    | 100.00% (0/0)   | 0.00% (0/4)     |
| test/PaymasterMagicSpendBase.sol | 0.00% (0/1)     | 0.00% (0/1)     | 100.00% (0/0)   | 0.00% (0/1)     |
| test/echidna/Fuzz.sol            | 0.00% (0/64)    | 0.00% (0/72)    | 0.00% (0/24)    | 0.00% (0/7)     |
| test/echidna/FuzzSetup.sol       | 0.00% (0/6)     | 0.00% (0/10)    | 100.00% (0/0)   | 0.00% (0/4)     |
| Total                            | 35.11% (46/131) | 34.39% (54/157) | 45.45% (20/44)  | 47.06% (16/34)  |

[wilsoncusack]

thank you!