feat: Expose concrete tracer implementation

        .gsub("{{ service }}", service_name)

    end

    # Returns the underlying tracer implementation from the tracing library in use.

    # This provides direct access to the native tracer API when LabKit's abstraction

    # is insufficient for advanced use cases.

    #

    # @example Using OpenTelemetry-specific APIs

    #   tracer = Labkit::Tracing.tracer

    #   tracer.start_span("custom-span") do |span|

    #     span.add_event("custom-event", attributes: { "key" => "value" })

    #   end

    #

    # @return [Object] The tracer implementation:

    #   - OpenTelemetry::SDK::Trace::Tracer when using OTLP connection

    #   - No-op tracer when tracing is not configured

    def self.tracer

      TracingUtils.tracer.tracer

    end

    # This will run a block with a span

    # @param operation_name [String] The operation name for the span

    # @param tags [Hash] Tags to assign to the span

end

```

### Direct Access to Underlying Tracer

When LabKit's abstraction doesn't provide the functionality you need, you can access the underlying tracer implementation directly using `Labkit::Tracing.tracer`:

```ruby

# Access the native tracer API

tracer = Labkit::Tracing.tracer

# Use OpenTelemetry-specific features when using OTLP connection

if Labkit::Tracing.otlp_connection?

  # tracer is an OpenTelemetry::SDK::Trace::Tracer instance

  tracer.start_span("custom-operation") do |span|

    span.add_event("processing_started", attributes: { "batch_size" => 100 })

    # Use OpenTelemetry-specific APIs

    span.record_exception(StandardError.new("test"))

    span.status = OpenTelemetry::Trace::Status.error("Failed")

  end

end

This is useful when you need:

- Library-specific APIs not exposed by LabKit (e.g., OpenTelemetry events)

- Advanced span manipulation or custom exporters

- Direct integration with third-party libraries that expect native tracer instances

## Instrumentation

### Rack Middleware

    end

  end

  describe ".tracer" do

    context "when using OpenTelemetry" do

      before do

        stub_const("ENV", ENV.to_hash.merge("GITLAB_TRACING" => "otlp://localhost:4318"))

        Labkit::Tracing::TracingUtils.instance_variable_set(:@tracer, nil)

      end

      it "returns the OpenTelemetry tracer" do

        tracer = described_class.tracer

        expect(tracer).to be_a(OpenTelemetry::Trace::Tracer)

      end

    end

    context "when using OpenTracing" do

      before do

        stub_const("ENV", ENV.to_hash.merge("GITLAB_TRACING" => "opentracing://jaeger"))

        Labkit::Tracing::TracingUtils.instance_variable_set(:@tracer, nil)

      end

      it "returns the OpenTracing global tracer" do

        tracer = described_class.tracer

        expect(tracer).to respond_to(:start_span)

        expect(tracer).to respond_to(:inject)

        expect(tracer).to respond_to(:extract)

      end

    end

    context "when tracing is not configured" do

      before do

        stub_const("ENV", ENV.to_hash.merge("GITLAB_TRACING" => nil))

        Labkit::Tracing::TracingUtils.instance_variable_set(:@tracer, nil)

      end

      it "returns a no-op tracer" do

        tracer = described_class.tracer

        expect(tracer).not_to be_nil

      end

    end

  end

  describe ".stacktrace_operations" do

    before do

      Labkit::Tracing.instance_variable_set(:@stacktrace_operations, nil)