`host-sp-comms` inventory probably should have a separate error code for bad device _contents_

[hawkw]

IPCC inventory lookups return the following error codes:

hubris/lib/host-sp-messages/src/lib.rs

Lines 261 to 271 in e744ccf

	pub enum InventoryDataResult {
	Ok,
	/// The given index is larger than our device count
	InvalidIndex,
	/// Communication with the device failed in a way that suggests its absence
	DeviceAbsent,
	/// Communication with the device failed in some other way
	DeviceFailed,
	/// Failed to serialize data
	SerializationError,
	}

Presently, DeviceFailed is what the SP will return when reading VPD from a device if the device returns an error, or if the data read from the device is malformed or corrupted. For example:

hubris/task/host-sp-comms/src/inventory/compute_sled_common.rs

Lines 133 to 136 in e744ccf

	// extract barcode!
	let identity = oxide_barcode::VpdIdentity::parse(&barcode[..n])
	.map_err(|_| InventoryDataResult::DeviceFailed)?;
	Ok(identity)

While testing #2229, @citrus-it and I saw that the host software will map the DeviceFailed result (code 3) to EIO, so it gets presented as an "I/O error":

gimlet-sn06 # ipcc inventory 0x48
metadata:
    version: 0x0
    entries: 0x49
J180/ID (72) -- Result: 3 [I/O error]

This doesn't feel quite right to me. I think we should introduce a new error code to represent "we read something from the device, but it didn't parse, had an invalid checksum, or an expected TLV-c tag was not present". Of course, adding new messages to the protocol will require coordination with the host side.