cardano-node: remove iohk-monitoring tracing backend

[jutaro]

Summary

Removes the legacy iohk-monitoring-based tracing infrastructure from
cardano-node, leaving trace-dispatcher as the sole tracing backend.

trace-dispatcher has been the production default since node 8.x. The old
iohk-monitoring path was retained during a transition period but is no longer
used or tested in production deployments. Removing it eliminates ~11 000 lines
of dead code and 9 transitive build dependencies.

What changed

Deleted (~8 100 lines, 15 modules):

• All of Cardano.Tracing.* — Config, HasIssuer, Metrics, Render,
  Shutdown, Startup, Tracers, and all OrphanInstances.* modules
  (Byron, Common, Consensus, HardFork, Network, Shelley)
• Cardano.Node.Configuration.Logging — the iohk-monitoring init layer
• Cardano.Node.Tracing.Compat — compatibility shim

Modified:

• Cardano.Node.Run — simplified to use only initTraceDispatcher; all
  legacy createLoggingLayer / setupTrace / Cardano.BM.* imports gone
• Cardano.Node.TraceConstraints — removes HasIssuer, ToObject, and
  related iohk-monitoring constraints
• cardano-node.cabal — drops iohk-monitoring, lobemo-backend-*,
  lobemo-scribe-systemd, ekg-wai, tracer-transformers, scientific
• Nix service config — removes legacy logging-layer options
• Benchmark profiles — "tracing_backend" updated to "trace-dispatcher"

Breaking change

Any node config still using "TracingBackend": "iohk-monitoring" or legacy
Logging config keys will need to be migrated to trace-dispatcher
configuration before upgrading. Refer to the trace-dispatcher migration guide.

Config options removed with iohk-monitoring

The following node configuration keys have no effect after the removal of the
iohk-monitoring tracing backend. All tracing is now handled exclusively by
trace-dispatcher.

Parsed by the node but silently ignored

These three keys are still accepted by the JSON parser to avoid hard failures
on existing configs, but have no effect:

Key	Previous effect
TurnOnLogging	Master on/off switch for the iohk-monitoring logging layer
TurnOnLogMetrics	Enabled/disabled node metrics collection via iohk-monitoring
UseTraceDispatcher	Chose between legacy (false) and trace-dispatcher (true) backend

Parsed by Cardano.Tracing.Config (module deleted)

Key	Previous effect
TracingVerbosity	Rendering verbosity: MinimalVerbosity / NormalVerbosity / MaximalVerbosity
TraceAcceptPolicy	Per-tracer on/off toggle (bool)
TraceBackingStore	"
TraceBlockFetchClient	"
TraceBlockFetchDecisions	"
TraceBlockFetchProtocol	"
TraceBlockFetchProtocolSerialised	"
TraceBlockFetchServer	"
TraceBlockchainTime	"
TraceChainDB / TraceChainDb	"
TraceChainSyncClient	"
TraceChainSyncBlockServer	"
TraceChainSyncHeaderServer	"
TraceChainSyncProtocol	"
TraceChurnMode	"
TraceConnectionManager	"
TraceConnectionManagerCounters	"
TraceConnectionManagerTransitions	"
TraceCsj	"
TraceDevotedBlockFetch	"
TraceDiffusionInitialization	"
TraceDNS / TraceDnsResolver / TraceDnsSubscription	"
TraceErrorPolicy / TraceLocalErrorPolicy	"
TraceForge / TraceForgeStateInfo	"
TraceGDD	"
TraceGsm	"
TraceHandshake / TraceLocalHandshake	"
TraceInboundGovernor	"
TraceInboundGovernorCounters	"
TraceInboundGovernorTransitions	"
TraceIpSubscription	"
TraceKeepAliveClient / TraceKeepAliveProtocol	"
TraceKesAgent	"
TraceLedgerPeers	"
TraceLocalChainSyncProtocol	"
TraceLocalConnectionManager	"
TraceLocalMux / TraceLocalMuxBearer / TraceLocalMuxChannel	"
TraceLocalRootPeers	"
TraceLocalServer	"
TraceLocalStateQueryProtocol	"
TraceLocalTxMonitorProtocol	"
TraceLocalTxSubmissionProtocol / TraceLocalTxSubmissionServer	"
TraceMempool	"
TraceMux / TraceMuxBearer / TraceMuxChannel	"
TracePeerSelection / TracePeerSelectionActions / TracePeerSelectionCounters	"
TracePeerSharingProtocol	"
TracePublicRootPeers	"
TraceSanityCheckIssue	"
TraceServer	"
TraceTxCounters	"
TraceTxInbound / TraceTxOutbound	"
TraceTxLogic	"
TraceTxSubmissionProtocol / TraceTxSubmission2Protocol	"

Read directly by the iohk-monitoring library

These keys were consumed by Cardano.BM.Configuration — the node never parsed
them itself. They are now entirely ignored:

Key	Previous effect
minSeverity	Global severity filter (Debug / Info / Notice / Warning / Error / Critical)
rotation	Log file rotation (rpLogLimitBytes, rpKeepFilesNum, rpMaxAgeHours)
setupBackends	Which backends to initialise (KatipBK, EKGViewBK, etc.)
defaultBackends	Default backend routing for namespaces
setupScribes	Log output targets (file, stdout, journald, trace-forwarder)
defaultScribes	Default scribe routing
hasEKG	Port for EKG web metrics interface
hasPrometheus	Host/port for Prometheus metrics endpoint
options.mapBackends	Per-namespace backend routing overrides
options.mapSubtrace	Per-namespace subtrace behaviour overrides
options.mapSeverity	Per-namespace severity filter overrides

Replacements in trace-dispatcher

The trace-dispatcher backend has its own equivalents for severity filtering
and output routing, configured under TraceOptions in the trace-dispatcher
config file. Refer to the trace-dispatcher documentation for the current config
format.

[jutaro]

The change in [Byron.hs:122] is:

Before:
( "txid" .= txId tx )
which relied on instance ToJSON (TxId (GenTx ByronBlock)) from the now-deleted Cardano.Tracing.OrphanInstances.Byron, which was:

instance ToJSON (TxId (GenTx ByronBlock)) where
toJSON = String . Text.take 8 . renderTxId
After:

( "txid" .= (Text.take 8 . renderTxId $ txId tx) )
The output is identical — both produce an 8-character hex string. The change just inlines the behavior that used to live in the deleted orphan instance, because that instance no longer exists.