protocol: add per-port DLStatus accessors, dedupe the unpacking

[leducp]

DLStatus::physicalLink/communication/loop(port) replace the flat PL_/COM_/LOOP_ portN unpacking that was repeated in toString() and Slave::countOpenPorts().

[github-actions]

File	Coverage	Lines	Branches
All files	82%	86%	79%	✅
lib/include/kickcat/Error.h	91%	100%	83%	✅
lib/include/kickcat/LockedRing.h	87%	94%	81%	✅
lib/include/kickcat/LoopbackSocket.h	81%	82%	80%	✅
lib/include/kickcat/SimulatorControl.h	82%	97%	68%	✅
lib/master/include/kickcat/AbstractLink.h	90%	80%	100%	✅
lib/master/src/Bus.cc	89%	90%	87%	✅
lib/master/src/CoE.cc	63%	72%	55%	❌
lib/master/src/Link.cc	98%	100%	97%	✅
lib/master/src/MailboxSequencer.cc	97%	100%	94%	✅
lib/master/src/MasterOD.cc	99%	99%	100%	✅
lib/master/src/Prints.cc	95%	95%	95%	✅
lib/master/src/Slave.cc	71%	86%	56%	❌
lib/master/src/dc.cc	77%	83%	70%	✅
lib/master/src/CoE/CiA/DS402/Drive.cc	51%	69%	34%	❌
lib/simulation/include/kickcat/simulation/DeviceApp.h	0%	0%	100%	❌
lib/simulation/include/kickcat/simulation/devices/Ds402Motor.h	0%	0%	0%	❌
lib/simulation/src/DeviceApp.cc	0%	0%	0%	❌
lib/simulation/src/SimulatedSlave.cc	0%	0%	0%	❌
lib/simulation/src/SimulatorControlServer.cc	89%	96%	82%	✅
lib/simulation/src/Topology.cc	73%	70%	76%	❌
lib/slave/src/AbstractESC.cc	92%	100%	84%	✅
lib/slave/src/AbstractEmulatedEEPROM.cc	0%	0%	0%	❌
lib/slave/src/ESMStates.cc	95%	98%	93%	✅
lib/slave/src/ESM.cc	95%	100%	90%	✅
lib/slave/src/EmulatedNetwork.cc	98%	99%	97%	✅
lib/slave/src/PDO.cc	94%	99%	90%	✅
lib/slave/src/ESC/EmulatedESC.cc	79%	84%	74%	✅
lib/slave/src/ESC/Lan9252.cc	0%	0%	0%	❌
lib/src/Frame.cc	96%	96%	97%	✅
lib/src/Mailbox.cc	90%	95%	85%	✅
lib/src/SIIParser.cc	85%	89%	81%	✅
lib/src/protocol.cc	89%	88%	90%	✅
lib/src/CoE/OD.cc	96%	97%	95%	✅
lib/src/CoE/protocol.cc	94%	94%	94%	✅
lib/src/CoE/CiA/DS402/StateMachine.cc	93%	94%	92%	✅
lib/src/CoE/mailbox/request.cc	83%	85%	80%	✅
lib/src/CoE/mailbox/response.cc	85%	91%	80%	✅
lib/src/ESI/Parser.cc	84%	88%	80%	✅
lib/src/ESI/SIIBuilder.cc	80%	92%	68%	✅
lib/src/EoE/protocol.cc	0%	0%	0%	❌

Minimum allowed coverage is 75%

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