RTIO Improvements

[teburd]

Several significant improvements to the existing RTIO subsys could make it more useful in common expected use cases

• [x] User mode support #51283
• [x] Dealing with a contended iodev/device #51772
• [x] Poll mode support with improved batching (non-interrupt driven iodevs) #62605
• [ ] Test covering rtio_submit to context with pending requests in the queue
• [ ] Simplify blocking consume call
• [ ] Simplify blocking submit call
• [x] Showcase of DMA usage (e.g. with a SPI driver supporting RTIO) SAM SPI uses DMA
• [ ] Flush Operation (wait on all prior events)
• [ ] Timeout Operation (wait on N prior events for T time)
• [ ] Deadline Operation (fail subsequent events if time T has passed)
• [x] Samples with real, easily accessible, hardware across multiple devices #55383
• [x] Experimental I2C support #56634
• [x] Experimental SPI support #56125
• [ ] RFC of DAI/I2S support
• [x] Equivalent to the io_uring Provided Buffer feature (buffer pool for reading) #56645
• [x] Move SPSC buffers to uninitialized sections to avoid rom memory usage #56432
• [ ] Delay Operations (wait T time before the next chained op) :new:
• [x] Move SPSC and MPSC lock free queues to an os library :new: (@nordic-krch) #63470
• [ ] Make semaphores construction time decisions for the context :new: (@nordic-krch)

[teburd]

@yperess added the provided buffer feature, let me know if that makes sense here or if it could use its own ticket