Split the RoT bootloader flash slot into stage0 and stage0next.
Always calculate the firmware measurement even if there is no valid image.
Add Stage0 and Stage0Next boot-time information to RotBootInfo.

lib/lpc55-rot-startup/src/{lib,images}.rs:
Refactored startup code to distinguish between a flash slot that is always measured
and the image it contains being valid or not.

Update the Update APIs and messages to accommodate update of the RoT's bootloader
while maintaining backward compatibility for Hubris updates.

An older control plane should be able to use its known update APIs
to bring a newer RoT or SP Hubris image back into conformance (roll-back).

Use conversion functions to isolate SP to MGS data structure conversion code.

Treat the boot loader as a separate component located in the RoT.
Add Stage0 and Stage0Next boot-time information to RotBootInfo.
Add Stage0 and Stage0Next to update-api.
lpc55-update-server: moving image format and location knowledge to images.rs

Add a versioned rot boot info request so that an older control plane can
upgrade/rollback newer images.
The existing rot_state and rot_boot_info need to remain stable for roll forward
and roll back to work when RoT version is newer than SP version.

Add Component* versions of APIs to allow selection of boot loader component.
Use Fwid type to represent the SHA3_256 digest in case we change digest algo someday.
Fwid includes padding bytes and any subsequent programmed pages in a flash slot,
so don't just call it a digest which can be misleading to people who might expect that
a hash of the bytes of an image would match the RoT report.

Old messages are still supported, e.g.:

$ faux-mgs ... --log-level=CRITICAL state
hubris archive: 8be7b8a5ebfc9313
serial number:
model:
revision: 0
base MAC address: 0e:1d:62:cd:cc:62
power state: A2
RotStateV2 {
 active: A,
 persistent_boot_preference: A,
 pending_persistent_boot_preference: None,
 transient_boot_preference: None
 slot_a_sha3_256_digest: 004fec2b8f77c091384b6c506230f18f24fc1db6c4de91a18e01ac3a244f015d,
 slot_b_sha3_256_digest: 6161bfd3b013e18fd45b539a5ddc9faafe2f3a43882832e49db3dffe58c36eb5,
}

New messages provide information needed to drive bootloader updates (see rot-boot-info below).
Image status has a more descriptive error code enum.

$ faux-mgs ... --log-level=CRITICAL rot-boot-info
RotBootInfo {V3(RotStateV3 {
 active: A,
 persistent_boot_preference: A,
 pending_persistent_boot_preference: None,
 transient_boot_preference: None
 slot_a_fwid: Sha3_256( 004fec2b8f77c091384b6c506230f18f24fc1db6c4de91a18e01ac3a244f015d ),
 slot_b_fwid: Sha3_256( 6161bfd3b013e18fd45b539a5ddc9faafe2f3a43882832e49db3dffe58c36eb5 ),
 stage0_fwid: Sha3_256( 62ebe27addfd99e6f6e2ba75302bbb96f8a2d4b2d01b270cbff2ee4e4a2c1280 ),
 stage0next_fwid: Sha3_256( 62ebe27addfd99e6f6e2ba75302bbb96f8a2d4b2d01b270cbff2ee4e4a2c1280 ),
slot_a_status: Ok(()),
slot_b_status: Ok(()),
stage0_status: Ok(()),
stage0next_status: Ok(()),
})}

The `stage0next` contents is not copied to `stage0` unless its current hash matches
the hash of a valid signed image found at boot time.

Stage0 cache size is 8192 to accommodate previous 6000+ byte bootloaders.
That can be reduced when rollback protection is implemented and old bootloaders
are expunged from any spares and systems in use.

Remove #[derive(Debug) statements whose deletion does not cause compile errors.