Added forge clean task

[lisandrasilva]

In some cases, when there are previous build artifacts in the out/ directory, the debugger behaves unexpectedly. This PR runs forge clean before running forge build for each debugging session that has the auto build flag set to true.

[RaoulSchaffranek]

I'm hesitant to automatically clean the out folder, especially because Kontrol stores its proofs there. Losing a compute-intensive proof would be unpleasant.

Can we further pin down the issue and investigate different solutions first?
We may not be sorting the build-info files correctly.
https://github.com/runtimeverification/simbolik-vscode/blob/master/src/foundry.ts#L95

[lisandrasilva]

The sorting is working correctly. But yes, let's pin down this issue, and if it happens again, I'll try to isolate it and investigate why it's happening.

Can we further pin down the issue and investigate different solutions first?
We may not be sorting the build-info files correctly.
https://github.com/runtimeverification/simbolik-vscode/blob/master/src/foundry.ts#L95