Migrate SPI controller operations to async

[floitsch]

Stacked on #3160.

Requires toitware/esp-idf#126, which adds a narrow public nonblocking SPI bus-acquire operation on top of the existing bus lock. That ESP-IDF PR is stacked on toitware/esp-idf#125.

This migrates ESP32 SPI controller transfers and explicit bus reservation away from blocking primitives.

Highlights:

• controller transfers are split into start and finish primitives; start queues with zero timeout and finish polls for the completed descriptor
• an allocation-free post-transaction callback wakes the waiting Toit task through the resource event queue
• native DMA buffers are allocated and populated before dispatch, and every synchronous error or retryable OOM path cleans up fully
• the operation remains protected across yields, including deadline handling, so dispatched transactions are always finalized
• explicit bus reservation uses try-acquire plus a Toit yield loop; a failed try rolls back only its own pending lock request
• short transmit-only transfers use persistent inline transaction storage, and zero-length transfers avoid null pointer arithmetic
• two-board tests verify scheduler progress during a deliberately slow transfer and repeatedly exercise reservation contention
• full SPI target and buffer-target suites pass on classic ESP32 and ESP32-S3, covering modes, bit order, speeds, DMA and non-DMA lengths, partial classic DMA words, overflow, re-arm, and maximum-size transfers

A recent upstream ESP-IDF checkout was checked as well. It still has no public finite-time or nonblocking SPI bus acquisition, so #126 remains necessary and intentionally follows the existing ESP-IDF lock API.

This is a complete-transaction API. Half-buffer streaming and watermark callbacks are deliberately not included.

[floitsch]

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📥 Commits

Reviewing files that changed from the base of the PR and between 2bbefb0 and 63cc407.

📒 Files selected for processing (7)

• lib/spi.toit
• src/compiler/propagation/type_primitive_spi.cc
• src/primitive.h
• src/resources/spi_esp32.cc
• src/resources/spi_esp32.h
• tests/hw/esp32/spi-buffer-target-shared.toit
• third_party/esp-idf

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