feat(generators): emit simulated host identity on every record (PIPE-1036)

[Dylan-M]

Stacked on #279

Proposed Change

Projects a resolved host identity onto every emitted record, so telemetry describes
a simulated fleet rather than the machine blitz runs on.

• resource.FromIdentity maps a SystemIdentity to its OpenTelemetry resource
  attributes: host.name, host.id, host.arch, the os.* set, host.ip[] /
  host.mac[], deployment.environment.name, and telemetry.source. Empty fields
  are omitted, and os.type carries the semconv value (macOS becomes darwin).
• Dispatch resolves one host per generator, keyed by component, and threads it into
  hostmetrics, traces, and all twelve log generators.
• SystemIdentity gains authentic OS release data, host.id, the full semconv
  host.arch set, and deployment tiers.
• host.image.* is a reserved hook and is not emitted.

With no environment configured, generators keep the process-hostname fallback, so
default output is unchanged.

Out of scope: per-worker host granularity. One host maps to one generator today; a
per-worker opt-in is a planned follow-up.

Validation: run blitz with an environment: block and the stdout output, and
confirm records carry host.name / host.id / os.type /
deployment.environment.name from the simulated fleet rather than the local host.
Tests cover the projection (full, sparse, and nil identities, the macOS os.type
mapping, the host.ip / host.mac arrays, and host.image.* never emitted),
per-generator identity, and dispatch wiring end to end.

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

• feat(config): reject invalid network CIDRs at environment load (PIPE-1002) #281
• feat(generators): emit simulated host identity on every record (PIPE-1036) #280 👈 (View in Graphite)
• feat(resource): support list-valued resource attributes (PIPE-1253) #279
• feat(datagen): environment foundations for simulated host identity (PIPE-1036) #278
• refactor(datagen): thread an injected logger, drop global-logger use (PIPE-1067) #277
• fix(datagen): return errors instead of panicking on developer-error input (PIPE-1003) #276
• feat(datagen): add IPv6 to NetworkIdentity and public emission (PIPE-1001) #275
• feat(datagen): add storage, network, and appliance-OS identities (PIPE-1035) #274
• main

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