Add support for lazy loading Pyroscope SDK from Application ClassLoader

[dordor12]

Fixes #46

Summary

This PR adds support for capturing Pyroscope SDK instances loaded by the Application ClassLoader, enabling integration with libraries like async-profiler-actuator-endpoint that provide profiling as a Spring Boot dependency.

Changes

New Configuration Option

Added otel.pyroscope.app.sdk.enabled configuration property (default: false):

-Dotel.pyroscope.app.sdk.enabled=true
# or
OTEL_PYROSCOPE_APP_SDK_ENABLED=true

Implementation

Uses OTel's bytecode instrumentation to lazily capture ProfilerSdk instances when they're constructed in the Application ClassLoader:

1. OtelProfilerSdkBridge - Made fields static, added appSdkEnabled flag and setSdkInstance() method. Cached reflection methods for better performance. The instrumentation only captures the SDK when appSdkEnabled=true.

2. ProfilerSdkInstrumentation - ByteBuddy instrumentation that hooks into ProfilerSdk constructor and calls OtelProfilerSdkBridge.setSdkInstance().

3. PyroscopeSdkInstrumentationModule - Registers the instrumentation and injects OtelProfilerSdkBridge as a helper class into the Application ClassLoader.

4. PyroscopeOtelConfiguration - Added appSdkEnabled configuration field.

5. PyroscopeOtelAutoConfigurationCustomizerProvider - Sets OtelProfilerSdkBridge.appSdkEnabled flag. SystemClassLoader loading is preserved as fallback.

How It Works

┌─────────────────────────────────────────────────────────────┐
│                  OTel Agent ClassLoader                      │
│  ┌─────────────────────────────────────────────────────────┐│
│  │  PyroscopeOtelSpanProcessor                             ││
│  │    → Uses OtelProfilerSdkBridge (static reference)      ││
│  └─────────────────────────────────────────────────────────┘│
└─────────────────────────────────────────────────────────────┘
                            │
                            │ (reflection via cached methods)
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                Application ClassLoader                       │
│  ┌─────────────────────────────────────────────────────────┐│
│  │  OtelProfilerSdkBridge (injected via Helper Injection)  ││
│  │    ← setSdkInstance() called on ProfilerSdk construct   ││
│  │    ← Only active when appSdkEnabled=true                ││
│  └─────────────────────────────────────────────────────────┘│
│                            ▲                                 │
│  ┌─────────────────────────────────────────────────────────┐│
│  │  io.pyroscope.javaagent.ProfilerSdk                     ││
│  │    (loaded as app dependency)                            ││
│  └─────────────────────────────────────────────────────────┘│
└─────────────────────────────────────────────────────────────┘

Files Changed

• src/main/java/io/otel/pyroscope/OtelProfilerSdkBridge.java - Static fields, appSdkEnabled flag, cached methods, setSdkInstance()
• src/main/java/io/otel/pyroscope/PyroscopeOtelConfiguration.java - Added appSdkEnabled
• src/main/java/io/otel/pyroscope/PyroscopeOtelAutoConfigurationCustomizerProvider.java - Sets appSdkEnabled flag
• src/main/java/io/otel/pyroscope/instrumentation/ProfilerSdkInstrumentation.java - New
• src/main/java/io/otel/pyroscope/instrumentation/PyroscopeSdkInstrumentationModule.java - New
• src/main/resources/META-INF/services/io.opentelemetry.javaagent.extension.instrumentation.InstrumentationModule - New

Usage

For applications using Pyroscope SDK as a dependency (e.g., with async-profiler-actuator-endpoint):

java -javaagent:opentelemetry-javaagent.jar \
     -Dotel.javaagent.extensions=pyroscope-otel.jar \
     -Dotel.pyroscope.app.sdk.enabled=true \
     -jar myapp.jar

Backwards Compatibility

• Default behavior unchanged (appSdkEnabled=false)
• When appSdkEnabled=false, instrumentation does not capture SDK
• Existing Java Agent mode (SystemClassLoader) continues to work as fallback
• Bundled mode continues to work

Testing

• Build passes
• Existing tests pass
• Manual testing with trace-span-profiles-example using async-profiler-actuator-endpoint

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