chore: Move global_hash.rs from turborepo-lib to turborepo-task-hash (#11355)
## Summary
Move `global_hash.rs` (~402 lines) from `turborepo-lib/src/run/` to
`turborepo-task-hash/src/` where it logically belongs.
- Reduces `turborepo-lib` by ~400 lines
- Global hash computation belongs with task hashing logic
- Part of ongoing modularization effort
## Changes
| File | Change |
|------|--------|
| `turborepo-task-hash/src/global_hash.rs` | Moved (via `git mv`) |
| `turborepo-task-hash/Cargo.toml` | Added dependencies |
| `turborepo-lib/src/run/mod.rs` | Updated imports |
| `turborepo-lib/src/run/error.rs` | Updated error import |
| `turborepo-lib/src/task_graph/visitor/mod.rs` | Updated imports |
| `turborepo-lib/src/task_hash.rs` | Added re-exports |
## Testing
- All 3 `turborepo-task-hash` tests pass
- All 253 `turborepo-lib` tests pass
- Used `git mv` to preserve file content exactly (including Unicode
characters in constants)