fw-update: reject mismatched EID in ItemUpdateManager dispatch

ItemUpdateManager::handleRequest declared its eid parameter as
mctp_eid_t /*eid*/ and dispatched purely on command. Combined with
AggregateUpdateManager iterating updateManagers in SoftwareIdentifier
(i.e. eid-then-component) order, whichever active ItemUpdateManager
came first claimed every FW-update response regardless of the inbound
EID. Two concurrent target updates on different EIDs would have all
responses funneled to the lower-EID manager.

Concretely: with an update on EID 12 in flight, starting an update
on EID 10 created ItemUpdateManager(10). EID 12's apply_complete was
then consumed by deviceUpdater10 and logged as if it belonged to EID
10 (device_updater.cpp:858 uses the deviceUpdater's own eid member).
EID 10 timed out on ActivateFirmware while EID 12's deviceUpdater
state was corrupted by the misrouted messages.

The per-ItemUpdateManager state (deviceUpdater, packageMap, dupFd,
inProgressActivation, ...) is already independent, and the shared
Handler<Request>/InstanceIdDb demux BMC->FD responses by
(eid, instanceId), so concurrent multi-EID target updates work
correctly once the responder path stops the cross-EID misrouting.

Add an explicit eid != this->eid early-return that yields
PLDM_FWUP_COMMAND_NOT_EXPECTED, letting AggregateUpdateManager fall
through to the next manager. Fold the !deviceUpdater branch into the
same early-return since it returns the same encoded response, and
convert the placement-new calls to std::start_lifetime_as<> to match
the rest of the codebase.

Tested on nvl32-obmc:
- Full bundle multipart update.
- Single target update.
- Back to back single-target updates.
- Full bundle update followed by a target update (previously flooded
  the journal with "invalid state when updating progress" and served
  data from the stale bundle DeviceUpdater; now routed correctly).
- Target update on a second PLDM device while an update on another
  device is in progress: both complete successfully.
- Target update on the same device while its update is in progress:
  rejected as expected.

Signed-off-by: Dhruv Rathi <rathidhruv04@gmail.com>
Change-Id: I390c54c82fc6405de37a06af6a8d0e80d31735d3