Add vm.unixTime to VmSafe interface

[Tudmotu]

Following foundry-rs/foundry#5952.
Adding vm.unixTime() cheatcode to VmSafe interface.
I tested this change manually on my machine.

[mds1]

Thanks! Sorry for the conflicts, but I just merged #464 which has two main changes:

1. It refactors the Vm file quite a bit to be more organized
2. It adds a test to verify we didn't accidentally change the Vm interfaces

Could you fix the conflicts on this branch as a result? We can put the new cheat in VmSafe under the "Filesystem" comment block. (I think we should rename that section to "OS and Filesystem", then move the two ffi cheats from the "External Interactions" into that section too, and delete "External Interactions". If you want to do that, that'd be awesome! No worries if not though)

Then you'll also need to update the failing test based on whatever the new interfaceId is

[Tudmotu]

Hi @mds1 thanks for the heads up.
I updated my branch with your asks. I was not sure what should I name the new "subsections".
I named them "Running executables" and "System information". Please let me know what you think:

I can change these if you'd like me to name them something else.

Edit: I now realize maybe I should have just used the "External Interactions" for the subsection title and group ffi & unixTime together? Let me know what you think.

[mds1]

Thank you!

[Tudmotu]

TIL what ffi means haha
Thanks for merging @mds1 🙏