feat(perf): add eBPF CPU profiler with ring buffer streaming

[jra3]

Summary

• Implements comprehensive eBPF-based CPU profiler using CO-RE technology
• Adds support for both hardware and software perf events with configurable sampling rates
• Aligns with cantstopwontstop philosophy - no Stop() methods, context-only cancellation

Key Features

✨ eBPF Profiler Implementation

• Ring buffer streaming for efficient kernel-to-userspace data transfer
• Stack trace collection with both user and kernel stacks
• Multiple perf event types: CPU cycles, cache misses, CPU clock, page faults
• Runtime configuration via ProfilerSetup interface

🎯 Context-Driven Lifecycle

• No Stop() method - automatic cleanup when context is cancelled
• No stopChan - uses only ctx.Done() for cancellation
• Automatic resource cleanup via dedicated goroutine

📊 Perf Event Enumeration

• Dynamic discovery of available perf events on the system
• Support for hardware, software, PMU, and cache events
• Graceful fallback for virtualized environments

Architecture Changes

Start(ctx) launches:
├── readRingBuffer goroutine (reads eBPF events)
├── collect goroutine (periodic profile collection)
└── cleanup goroutine (waits and cleans up automatically)

Testing

• Comprehensive test suite for profiler functionality
• Integration tests for hardware and virtualized environments
• Stability tests for long-running profiling sessions

Documentation

• Added detailed profiler testing methodology guide
• Perf event enumeration documentation
• Hardware testing guidelines for bare metal validation

Related Issues

Closes:

• feat(profiler): Implement BPF ring buffer for profiler #125 - Implement BPF ring buffer for profiler
• feat(profiler): Define 32-byte profile event structure #126 - Define 32-byte profile event structure
• feat(profiler): Add ring buffer tests and benchmarks #128 - Add ring buffer tests and benchmarks
• feat(profiler): Add memory stability tests #132 - Add memory stability tests
• Expand kernel version support for some eBPF collectors #142 - Expand kernel version support (satisfied with 5.15+ requirement)