test: enable telemetry tests in server mode (#3927)

# What does this PR do?
- added a server-based test OLTP collector

## Test Plan
CI

tests/integration/telemetry/collectors/in_memory.py

@@ -0,0 +1,93 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+"""In-memory telemetry collector for library-client tests."""
+
+from typing import Any
+
+import opentelemetry.metrics as otel_metrics
+import opentelemetry.trace as otel_trace
+from opentelemetry import metrics, trace
+from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.metrics.export import InMemoryMetricReader
+from opentelemetry.sdk.trace import TracerProvider
+from opentelemetry.sdk.trace.export import SimpleSpanProcessor
+from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
+
+import llama_stack.core.telemetry.telemetry as telemetry_module
+
+from .base import BaseTelemetryCollector, SpanStub
+
+
+class InMemoryTelemetryCollector(BaseTelemetryCollector):
+    def __init__(self, span_exporter: InMemorySpanExporter, metric_reader: InMemoryMetricReader) -> None:
+        self._span_exporter = span_exporter
+        self._metric_reader = metric_reader
+
+    def _snapshot_spans(self) -> tuple[Any, ...]:
+        spans = []
+        for span in self._span_exporter.get_finished_spans():
+            trace_id = None
+            span_id = None
+            context = getattr(span, "context", None)
+            if context:
+                trace_id = f"{context.trace_id:032x}"
+                span_id = f"{context.span_id:016x}"
+            else:
+                trace_id = getattr(span, "trace_id", None)
+                span_id = getattr(span, "span_id", None)
+
+            stub = SpanStub(
+                span.name,
+                span.attributes,
+                getattr(span, "resource", None),
+                getattr(span, "events", None),
+                trace_id,
+                span_id,
+            )
+            spans.append(stub)
+
+        return tuple(spans)
+
+    def _snapshot_metrics(self) -> Any | None:
+        data = self._metric_reader.get_metrics_data()
+        if data and data.resource_metrics:
+            resource_metric = data.resource_metrics[0]
+            if resource_metric.scope_metrics:
+                return resource_metric.scope_metrics[0].metrics
+        return None
+
+    def _clear_impl(self) -> None:
+        self._span_exporter.clear()
+        self._metric_reader.get_metrics_data()
+
+
+class InMemoryTelemetryManager:
+    def __init__(self) -> None:
+        if hasattr(otel_trace, "_TRACER_PROVIDER_SET_ONCE"):
+            otel_trace._TRACER_PROVIDER_SET_ONCE._done = False  # type: ignore[attr-defined]
+        if hasattr(otel_metrics, "_METER_PROVIDER_SET_ONCE"):
+            otel_metrics._METER_PROVIDER_SET_ONCE._done = False  # type: ignore[attr-defined]
+
+        span_exporter = InMemorySpanExporter()
+        tracer_provider = TracerProvider()
+        tracer_provider.add_span_processor(SimpleSpanProcessor(span_exporter))
+        trace.set_tracer_provider(tracer_provider)
+
+        metric_reader = InMemoryMetricReader()
+        meter_provider = MeterProvider(metric_readers=[metric_reader])
+        metrics.set_meter_provider(meter_provider)
+
+        telemetry_module._TRACER_PROVIDER = tracer_provider
+
+        self.collector = InMemoryTelemetryCollector(span_exporter, metric_reader)
+        self._tracer_provider = tracer_provider
+        self._meter_provider = meter_provider
+
+    def shutdown(self) -> None:
+        telemetry_module._TRACER_PROVIDER = None
+        self._tracer_provider.shutdown()
+        self._meter_provider.shutdown()