Update rp2.asm_pio decorator typestub with execctrl and side_pindir parameters

[Copilot]

Updates the reference typestub for rp2.asm_pio decorator to include the new parameters proposed in MicroPython PR #18133.

Changes

New asm_pio decorator parameters:

• execctrl=0 - Configures additional execution control options. Can be used with constants like PIO.STATUS_TXLEVEL + n to trigger status checks based on FIFO thresholds.
• side_pindir: Optional[bool] = None - When set to True, configures .side() modifiers to be used for pin directions instead of pin values (the default when False).

New PIO constants:

• PIO.STATUS_TXLEVEL = 0 - Status value for TX FIFO level threshold
• PIO.STATUS_RXLEVEL = 32 - Status value for RX FIFO level threshold
• PIO.STATUS_IRQ = 64 - Status value for IRQ flags

Usage Example

With these updates, developers can now use advanced PIO features like:

@rp2.asm_pio(execctrl=rp2.PIO.STATUS_TXLEVEL + 5, side_pindir=True)
def advanced_program():
    mov(y, status)
    jmp(not_y, "skip")
    irq(rel(0))
    label("skip")

This enables interrupt generation when the TX FIFO has fewer than 5 words left, and configures side-set pins to control directions rather than values.

Backward Compatibility

All existing code remains fully compatible - these are optional parameters with sensible defaults that match the current behavior.

Files Updated

• reference/micropython/rp2/__init__.pyi - Main reference typestub
• reference/micropython/rp2/PIO.pyi - Added STATUS constants
• stubs/micropython-v1_27_0_preview-docstubs/rp2/__init__.pyi - Future version consistency
• stubs/micropython-v1_27_0_preview-docstubs/rp2/PIO.pyi - Future version constants

Fixes the issue by providing proper type hints for the enhanced PIO assembler functionality that will be available in future MicroPython releases.

Fixes #834

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