Add new read_setup() for control endpoints

[ianrrees]

Background can be found at atsamd-rs/atsamd#738 .

The USB spec says that the SETUP transactions used with control endpoints must always be accepted by the device [1], and at least in the Microchip SAMD21's USB peripheral that behaviour is handled in hardware [2]. We've observed that some hosts will send an OUT ZLP, followed very shortly by a SETUP for a new transaction - on the SAMD21 parts this results in the OUT data (none, in this case) being overwritten by SETUP, which in the existing implementation results in an overflow error (since read() was called with a zero length slice for the OUT ZLP, but >0 bytes are available from the SETUP that overwrote it). The user-observable result is that the device fails to enumerate at all on some hosts, or sporadically on others.

In light of this, it seems the control pipe code needs some way to differentiate reads of OUT data from reads of SETUP data. This PR changes the existing read() methods to return an error if SETUP data is present, making it specific to OUT data, and adds a new read_setup() method specifically for reading SETUP data.

Most of the commits/diff here are work on the test framework, to add a new test that resets the device and times how long it takes to re-enumerate. The test is a bit crude, but seems to validate the changes to the read methods.

[1] USB 2.0 spec section 5.5.5 Control Transfer Data Sequences:

If a Setup transaction is received by an endpoint before a previously initiated control transfer is completed,
the device must abort the current transfer/operation and handle the new control Setup transaction. A Setup
transaction should not normally be sent before the completion of a previous control transfer. However, if a
transfer is aborted, for example, due to errors on the bus, the host can send the next Setup transaction
prematurely from the endpoint’s perspective.

[2] SAMD21 datasheet DS40001882H section 32.6.2.6 Management of SETUP Transactions. The key thing here is that the data is copied in to the buffer regardless of BK0RDY.

[ianrrees]

@ithinuel - this is the PR discussed the other day in Matrix, I've put the corresponding atsamd-rs changes here, and test class implementations for SAMD21 and SAMD51 are here

[ianrrees]

@9names ran some tests of this with Raspberry Pi 5 host and SAMD21, confirming the problem (enumeration being unreliable) and that this appears to resolve it.

While confirming the problem, 9names saw the new test case error out in an unexpected way - reporting Entity not found - I think that might require a bit more work to make the enumeration time test more reliable.

[ianrrees]

Sorry, I've not had an opportunity to look at the test code changes here, and probably won't be able to test Rust USB stuff until mid December at earliest. Since the test stuff isn't really critical, I'd like to proceed with this PR so that implementors can do their part.