ports/nrf: Add Zephyr BLE with on-core controller support.

[andrewleech]

Summary

Adds Zephyr BLE support to the nRF port (PCA10056 DK and PCA10059 dongle) using the Zephyr BLE host stack with an on-core BLE controller. Unlike the RP2 and STM32 integrations which rely on external BLE controllers (CYW43, STM32WB M0+), the nRF52840 runs the Zephyr BLE controller directly on the application core alongside MicroPython.

This required building the full Zephyr BLE controller (link layer, radio HAL, ticker) against the HAL shim layer, plus IRQ management shims that bridge Zephyr's irq_connect_dynamic() / irq_enable() / irq_disable() to NVIC operations. The controller's radio ISR and ticker timing run at hardware interrupt priority while the host stack processes events cooperatively from the main task via mp_sched_schedule_node().

Also adds SysTick, soft timer, and PendSV dispatch infrastructure to the nRF port which were previously missing and are needed for the scheduler-based BLE polling.

Depends on #21.

Testing

12/12 BLE multitests passing on nRF52840 DK with PYBD as central, and 12/12 Z2Z (DK as peripheral + PCA10059 dongle as central). Bond persistence test passes via the SUSPENDED mode reactivation path (on-core controller can't cleanly restart after bt_disable()).

Performance: ~35ms/notification (GATT), ~2184 B/s (L2CAP) with PYBD; ~25ms/notification, ~2681 B/s Z2Z.

428KB flash (42%), ~220KB RAM (84%) on PCA10056.

Trade-offs and Alternatives

The on-core controller means bt_disable() can't cleanly shut down and restart the radio — the Zephyr controller wasn't designed for this. Instead, ble.active(0) enters a SUSPENDED state that stops advertising/scanning/connections but leaves the stack running. This wastes some power but avoids the need for a full chip reset to reinitialise.

The hci_driver_wrapper.c wraps Zephyr's hci_driver.c to expose file-scope variables for RX polling, avoiding a submodule patch.

Generative AI

I used generative AI tools when creating this PR, but a human has checked the code and is responsible for the description above.