feat(o11y): lifecycle startup-latency metrics via new runtime weaver registry (PIPE-1066)

[Dylan-M]

Proposed Change

Adds startup-latency metrics through a new internal/runtime/monitoring weaver registry:
blitz.module.startup.duration (per module), blitz.session.startup.duration, and the
process-level blitz.startup.duration. runtime.New now takes a MeterProvider and
returns an error; both call sites (the embed runner and service.New) are updated.
runtime.Start records the per-module and session latencies. The main entry point
records the process-level latency best-effort, so a metric-build failure never fails
startup.

How to validate

• Run blitz (startup latency is recorded once at startup, so any config works):
  go run ./cmd/blitz --generator-type apache-common --generator-apache-common-rate 1s --output-type stdout --metrics-port 9100
• Confirm the three startup series appear:
  curl -s localhost:9100/metrics | grep -E 'blitz_module_startup_duration|blitz_session_startup_duration|blitz_startup_duration'.
• go test ./internal/runtime/... covers the recording and the NewMetrics error path.
• make generate-o11y-check regenerates the weaver metric code and fails on any drift from
  the committed files (needs Docker, matching CI).

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 👈 (View in Graphite)
• feat(o11y): bring stdout/nop outputs fully into the self-telemetry spine (PIPE-1066) #290
• 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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