Covers message extraction (body, message attribute, eventName, default),
severity→level mapping (error/fatal→ERROR, warn→WARN, others→DEBUG),
stack trace extraction, attribute→tag conversion, timestamp fallback,
multiple records, and forceFlush.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

An empty flush (no pending batches) is a success — there was nothing to
upload, so the operation trivially succeeded. Initialising result=true
instead of false makes flush() consistent with that expectation and
allows forceFlush()/flush() callers to distinguish "nothing to do" from
a real upload failure.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Implements the distributions payload type per the telemetry spec:
- TelemetryDistribution with its own Namespace (tracers/profilers/rum/appsec)
  and Series carrying raw sample values ([Double]) rather than [timestamp,value] pairs
- Wired into TelemetryRequestType enum, TelemetryMessageBatch decoder, and TelemetryApi
- sendDistributions() added to TelemetryApi protocol and TelemetryApiService
- TelemetryExporterTests extended to cover distributions round-trip and mixed-type batches

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Histogram types carry sampled data, so they map naturally to the
distributions request type rather than the generate-metrics count/sum pair.

Conversion strategy:
- Histogram (explicit boundaries): reconstruct approximate sample values
  using bucket midpoints; edge buckets use min/max when available.
- ExponentialHistogram: geometric midpoint of each exponential bucket
  (base^(offset+i+0.5) where base = 2^(2^-scale)).
- Summary: kept as generate-metrics count+sum (already pre-aggregated).

TelemetryMetricExporter.export(metrics:) now emits a TelemetryMetric
payload for scalar types and a separate TelemetryDistribution payload for
histogram types when both are present in the same batch.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

When a histogram's underflow (first) bucket has no recorded min, use the
first explicit boundary as the representative value instead of 0. A value
in the underflow bucket is <= boundaries[0], so the boundary itself is a
closer approximation than 0 — especially for histograms whose boundaries
don't start near zero.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

The exporter previously declared cumulative temporality for all instruments.
Under cumulative, OTel emits running totals since process start on every
collection, which is wrong for the DD targets:
- DD `count` sums submitted values per interval, so feeding it cumulative
  snapshots inflates the count.
- `distributions` expect the interval's raw samples, so reconstructing from
  cumulative bucket counts re-emits the entire sample set each cycle.

Mirror OTel's deltaPreferred() selector: up/down counters (mapped to DD
gauge) stay cumulative so the current running total is reported; counters,
histograms, and gauges request delta.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Read the telemetry namespace from each metric's Resource (attribute key
"dd.telemetry.namespace") and set it as the per-series namespace override.
This lets a meter provider route its metrics to a specific namespace without
a dedicated exporter instance. When the attribute is absent or its value
isn't valid for the target payload (e.g. a generate-metrics-only namespace
on a distribution), the override is omitted and the exporter's configured
payload-level namespace applies.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Replace the ad-hoc TelemetryMetricResourceKeys constant and MetricConversion
namespace helpers with a typed `Resource.telemetryNamespace` getter/setter in
OpenTelemetry+Extensions, matching the existing applicationName/environment/etc.
accessors. The converter now reads metric.resource.telemetryNamespace and maps
it to the payload-specific Namespace enum via init(rawValue:).

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Split the single string-based telemetryNamespace into two typed accessors,
one per payload type with its own resource key:
- telemetryMetricNamespace: TelemetryMetric.Namespace?
  (key "dd.telemetry.metric.namespace")
- telemetryDistributionNamespace: TelemetryDistribution.Namespace?
  (key "dd.telemetry.distribution.namespace")

Getters/setters work directly with the enum types (no String at the call
site), and the separate keys let metrics and distributions carry independent
namespaces — necessary since the two enums accept different value sets.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>