feat: add --diagnostics command exercising IDeviceDiagnostics

[tylerkron]

Summary

Adds a --diagnostics CLI command that exercises the full IDeviceDiagnostics surface added in daqifi-core#266. Useful as a one-shot bench check of the firmware's logging & performance-counter queries.

It connects + initializes, then runs each query and prints results:

• SYSTem:ERRor:COUNt? — error-queue depth
• SYSTem:MEMory:FREE? — heap / sample-pool diagnostics
• SYSTem:STReam:STATS? — streaming performance counters
• SYSTem:LOG:TEST → SYSTem:LOG? — inject then read the system log
• SYSTem:LOG:CMDHistory? — recent SCPI command history
• SYSTem:LOG:LEVel STREAM,2 — set a runtime log level (echoes applied level + ceiling)
• SYSTem:LOG:CLEar — clear the log buffer

Each step is isolated (one failed/unsupported query is reported but doesn't abort the rest); the process exits non-zero if any step fails. All operations are non-destructive (the only state touched — log buffer, runtime log level — is volatile and resets on reboot).

⚠️ Dependency — draft

This depends on the IDeviceDiagnostics API from daqifi-core#266, which is newer than the published Daqifi.Core 0.24.0 package this app references by default. Until a release with diagnostics ships:

• The default build fails (Daqifi.Core.Device.Diagnostics not found in 0.24.0).
• Build/run against a local core checkout:

  dotnet build Daqifi.Core.Cli.csproj -c Release -p:DaqifiCoreProjectPath=<path-to>/Daqifi.Core.csproj
  

Before merging: wait for core #266 to merge + a new Daqifi.Core package to publish, then bump the PackageReference version in Daqifi.Core.Cli.csproj and undraft.

Bench-tested

Built against the core #266 branch and run against a real device (NQ over USB serial, /dev/cu.usbmodem101) — exit code 0, all eight queries succeeded:

== Memory diagnostics (SYSTem:MEMory:FREE?) ==
  HeapFree=13712 / HeapTotal=75000 (HeapUsed=61288, MinEverFree=13712)
  SamplePool: count=1100 inUse=0 maxUsed=0
  (14 fields total)

== Stream stats (SYSTem:STReam:STATS?) ==
  ... (43 counters total)

== Read system log (SYSTem:LOG?) ==
  1 entries:
    Test error message            # only ERROR-level survives the default log level

== Command history (SYSTem:LOG:CMDHistory?) ==
  10 commands: ...

== Set log level (SYSTem:LOG:LEVel STREAM,2) ==
  STREAM: level=2 (ceiling 3)

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