support positional `--mp` parameter for `forge test`

[zhiqiangxu]

This PR tries to fix this issue, users can now simply type forge test path_to_sol to run test.

[zhiqiangxu]

It seems my vscode uses a different format which fails test / rustfmt, what should I do to make it consistent with foundry?

[grandizzy]

It seems my vscode uses a different format which fails test / rustfmt, what should I do to make it consistent with foundry?

pls see https://github.com/foundry-rs/foundry/blob/master/CONTRIBUTING.md#resolving-an-issue for vscode settings and commands to check locally

[zhiqiangxu]

@zerosnacks Do you have any additional feedback or suggestions for this PR?