fix: allow multiple threads to share hash tracker (#6012)
### Description
When executing a task, it might need to update the hash tracker with:
- cache status
- expanded output globs
or it might need to query the env vars.
Since task execution happens on multiple threads we need to ensure that
the state portion can be shared between threads. This is achieved with a
good ol' `Arc<Mutex>` around the mutable state. In Go we do the same
thing, but with a `RWLock`, this can be ported in the future if we find
that there's enough contention for the mutex. (I'm currently unconvinced
this is necessary considering how infrequently reads happen)
I'm holding off on the cache status portion of the hash tracker since
that depends on run summary code and I don't want to conflict with #5833
### Testing Instructions
New test ensures that we can share the underlying state between threads
since it is `Send + Sync`.
Closes TURBO-1350
Co-authored-by: Chris Olszewski <Chris Olszewski>
