Wire up TIM2 handler

[xarantolus]

Right now, after ~71 minutes or ~2^32 us, the system gets stuck because it's always interrupted by TIM2, and the interrupt keeps happening since we didn't clear it so far.

Also note that I changed the handler to use the HAL functions for clearing.

[Copilot]

Pull request overview

This PR wires up a HAL-owned TIM2 overflow IRQ handler so the monotonic timer overflow interrupt is acknowledged/cleared, preventing the system from getting stuck after ~2³² µs (~71 minutes) of uptime on STM32L4.

Changes:

• Add a kernel → HAL callback (init_irqs) so the HAL can register required IRQ handlers during boot.
• Register a monotonic-timer overflow handler (selected via /chosen/osiris,monotonic-timer) that calls into the C TIM2 overflow handler.
• Switch the TIM2 overflow handler to clear the update flag via STM32 LL helpers and add the chosen node property for the Nucleo L4R5ZI board.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/lib.rs	Calls HAL init_irqs(...) during kernel init.
src/irq.rs	Exposes HAL API IRQ handler type and adds a safe registration wrapper for HAL init.
machine/cortex-m/st/stm32l4/interface/export.h	Exports tim2_hndlr() for Rust bindings.
machine/cortex-m/st/stm32l4/interface/clock.c	Clears TIM2 update flag via LL API in the IRQ handler.
machine/cortex-m/src/stub.rs	Adds a no-op init_irqs for the stub machine.
machine/cortex-m/src/native.rs	Registers the monotonic overflow IRQ handler based on DT chosen property.
machine/api/src/lib.rs	Extends Machinelike with init_irqs and defines IRQ registration types.
boards/nucleo_l4r5zi.dts	Selects TIM2 (&timers2) as the monotonic timer via /chosen.

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