Refactor the scheduler so all scheduleable work is wrapped in Arc<Work>,
replacing the previous per-CPU wait_q design where sleeping tasks were
bound to a specific CPU. Wakers now hold direct Arc<Work> references and
can re-enqueue tasks on any CPU upon wakeup.
Key changes:
- Add Work struct wrapping OwnedTask with an AtomicTaskState and
scheduler metadata (SchedulerData), replacing the old SchedulableTask.
Remove Task::state (Arc<SpinLock<TaskState>>). Work::state is now the
single source of truth for task state.
- Rewrite the run queue using BinaryHeap-based eligible/ineligible split
(EEVDF) with a dedicated VClock, replacing the BTreeMap linear scan.
Extract vclock into its own module.
- Rewrite wakers to hold Arc<Work> directly instead of looking up tasks
by TaskDescriptor from TASK_LIST.
- Replace lock-based sleep transitions in uspc_ret with atomic CAS
(try_sleep_current) that correctly detects concurrent Woken state.
- Simplify least-tasked-CPU metric to use only run-queue weight, since
sleeping tasks are no longer bound to any CPU.
- Add current_work() accessor.
Replace the single `SmallRng` with a proper two-layer RNG architecture:
- Global BLAKE2s-256 entropy pool that accumulates entropy and gates
seed extraction behind a 256-bit threshold.
- Per-CPU ChaCha20Rng instances that are lazily seeded from the pool on
first use and periodically reseed every 1 MB by XOR-ing a fresh BLAKE2
extract with 32 bytes of their own output.
The /dev/random chardev uses fill_random_bytes directly instead of
routing through the syscall layer.
Rework uname to avoid hardcoded datetime and add unit tests
Restructure `uname` so that:
- there is an internal function that does the main logic and can be tested by unit tests
- Generate an env var in build.rs that is the actual build datetime timestamp
- Avoid hardcoded date in the version string
- Use the timestamp in the building of `uname` response, so the data is the actual build time
- add a simple unit test for the sysname field
- add more complex test for the version field that checks the date formatting (not exhaustively)
NOTE: The build timestamp can be used by any other function, syscall or part of the code if required.
