class QueueRequests

Submit Requests to queue. Processed starting with the 0th Request. Submitting a vector of

Requests allows for pre-buffering.

Clients are responsible for cache management and ensuring cache coherency.

After read requests:

- Call zx_cache_flush with ZX_CACHE_FLUSH_DATA | ZX_CACHE_FLUSH_INVALIDATE on buffers that

have been mapped by the client.

- Call zx_vmo_op_range with ZX_VMO_OP_CACHE_CLEAN_INVALIDATE on all other buffers.

Note that writing to any portion of a buffer before OnCompletion is called for that buffer

can corrupt the received data.

Before write requests:

- Call zx_cache_flush with ZX_CACHE_FLUSH_DATA on buffers that have been mapped by the

client.

- Call zx_vmo_op_range with ZX_VMO_OP_CACHE_CLEAN on all other buffers.

Requests may be pre-buffered. In other words, requests may be queued for data that is not

present/ready in the buffer yet. The USB Endpoint Server consuming requests does not care

if the data in the buffer is ready or not and will always process requests on schedule. It

is the responsibility of the USB Endpoint Client that submits requests to ensure that data

is ready on schedule.

* Definition of "on schedule" varies for different endpoints and controllers. In general,

this will be communicated by the `lead_time` parameter returned by `GetInfo`.