feat(o11y): bring stdout/nop outputs fully into the self-telemetry spine (PIPE-1066)

[Dylan-M]

Proposed Change

Pulls the last two outputs into the spine. stdout and nop now take a TelemetrySettings,
build per-instance metrics, and share the bridged logger like every other output. stdout
gets a gated blitz.output.stdout.flush span around the real I/O. nop gets a
records-written counter but no span, since it is a synchronous no-op already inside the
emit span. The counter lets a load run measure how many records a nop output absorbed.

How to validate

• Run stdout with per-batch spans on, pointing at a collector:
  go run ./cmd/blitz --generator-type apache-common --generator-apache-common-rate 1s --output-type stdout --metrics-port 9100 --telemetry-traces-otlpendpoint localhost:4317 --telemetry-traces-insecure --telemetry-traces-perbatchspans
• Confirm stdout's self-metrics (curl -s localhost:9100/metrics | grep blitz_output_) and
  a blitz.output.stdout.flush span at the collector.
• Change --output-type nop and confirm its records-written counter climbs:
  curl -s localhost:9100/metrics | grep blitz_output_entries_received.
• go test ./output/nop/... ./output/stdout/... covers metrics, the flush span, and the
  nop counter.

Checklist

• Changes are tested
• CI has passed

[Dylan-M]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• fix(o11y): record output request + HEC ACK-poll latency in ms (PIPE-1404) #292
• feat(o11y): lifecycle startup-latency metrics via new runtime weaver registry (PIPE-1066) #291
• feat(o11y): bring stdout/nop outputs fully into the self-telemetry spine (PIPE-1066) #290 👈 (View in Graphite)
• feat(o11y): per-batch output send spans + HEC ACK-poll span (PIPE-1066) #289
• feat(o11y): wire fix generator into the self-telemetry spine (PIPE-1066) #288
• feat(o11y): self-logs via shared entry-point zap->OTel bridge + OTLP log export (PIPE-1066) #287
• feat(o11y): self-tracing via runtime spans, adapter emit spans, and OTLP trace export (PIPE-1066) #286
• feat(o11y): per-instance metrics via injectable MeterProvider, drop package globals (PIPE-1066) #285
• feat(embed): add TelemetrySettings provider bundle + NopTelemetry (PIPE-1066) #284
• main

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