Enable SMP with per-hart runtime state on RISC-V

[codingskynet]

Summary

• Bring up secondary RISC-V harts using a boot-hart release protocol.
• Add PerCore state for hart IDs, current threads, idle contexts, and dedicated panic stacks.
• Preserve the kernel tp value across user-mode traps and thread migration.
• Initialize trap and timer state independently on each hart.
• Run the scheduler on every hart and expose the current hart ID through a syscall.
• Add a MicroPython smp.hart_id() module and SMP smoke coverage.
• Keep a separate emergency panic stack for the early boot phase before PerCore is installed.
• Remove the obsolete U-mode trap stack overflow smoke test.
• Update the Rust toolchain and LLVM tools component.

Testing

• make check
• make run DEBUG=1 FEATURES=smoke-kernel-stack-overflow
• Verified the expected kernel stack overflow panic under 4-hart QEMU.

[codingskynet]

TODO: 나중에는 idle thread를 per-core 단위로만 관리할 것. 지금은 임의의 cpu core가 계속 임의의 thread를 실행할 수 있도록, 항상 idle thread를 코어 개수만큼 생성한 것과 같음 어차피 지금 안 고치면 안 돌아가서 고침