test: increase Checkpoints lib coverage

[0xrajath]

Motivation:

Currently the coverage report for the Checkpoints Library shows up as 0%.
We need to fix it by refactoring the Checkpoints Mock in Checkpoints.t.sol as stated in foundry-rs/foundry#3128 (comment)

Modifications:

• Refactoring Checkpoints Mock from:

contract LibHelper {
    function increment(uint256 a) external returns (uint256 r) {
        r = Lib.increment(a);
    }
}

to

contract LibHelper {
    function increment(uint256 a) external returns (uint256) {
        uint256 r = Lib.increment(a);
        return r;
    }
}

• Removing using for notation in Checkpoints Mock
• Setting coverage threshold back to 80%

Result:

Increased code coverage for Checkpoints Library. Closes #184

[dd0sxx]

nice work!

[dd0sxx]

do you want to change CI to fail again if coverage is below 80/90%?

[0xrajath]

do you want to change CI to fail again if coverage is below 80/90%?

Oh yeah good point. Will do

[github-actions]

Coverage after merging rajath/fix-checkpoints-coverage into main will be

90.12%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
VertexAccount.sol	100%	100%	100%	100%
VertexCore.sol	90.55%	87.93%	80%	93.50%	264, 271–272, 272, 272–273, 298, 305–306, 306, 306–307, 408, 480, 484
VertexFactory.sol	100%	100%	100%	100%
VertexLens.sol	100%	100%	100%	100%
VertexPolicy.sol	81.25%	66.67%	84.38%	82.98%	117, 119–121, 121, 121–122, 141–142, 177–178, 180–181, 271–272, 277, 302, 327, 334, 343, 381, 95
VertexPolicyMetadata.sol	100%	100%	100%	100%
VertexStrategy.sol	97.96%	83.33%	100%	100%	149
src/lib
Checkpoints.sol	79.68%	72.22%	94.44%	80.87%	105, 204, 216–217, 258–260, 260, 260–261, 263, 266, 294–295, 333–335, 337–339, 341–343, 345–347, 349–351, 353–355, 361–362, 380, 389, 53
ERC721NonTransferableMinimalProxy.sol	92.75%	95.45%	81.82%	94.44%	117, 189, 44