feat(gdb): add GDB RSP backend for GPU-aware debugging (v0.10.0)

Implement TraceSmith as a GDB remote debugging backend with GPU awareness:

Core Components:
- RSPHandler: GDB Remote Serial Protocol server implementation
- ProcessController: Process control via ptrace (Linux) / Mach API (macOS)
- GPUDebugEngine: GPU state management, breakpoints, and trace replay

Features:
- Automatic GPU state capture at CPU breakpoints
- GPU kernel call history tracking
- GPU memory monitoring via MemoryProfiler integration
- Trace capture/save/load with SBT format
- Trace replay debugging with step/seek controls
- GPU-specific breakpoints (kernel launch, memcpy, memset)
- Custom GDB monitor commands (ts status, ts kernels, ts trace, etc.)

Platform Support:
- Linux: Full support via ptrace
- macOS: Basic support via Mach API (partial ptrace)

Test Results:
- 85 unit tests passing (RSP protocol, GDB types, GPU debug engine)

Author: chenxingqiang

CMakeLists.txt

@@ -188,6 +188,12 @@ add_subdirectory(src/state)
 add_subdirectory(src/replay)
 add_subdirectory(src/cluster)
 
+# GDB RSP backend (Linux only for now)
+option(TRACESMITH_BUILD_GDB "Build GDB RSP backend" ON)
+if(TRACESMITH_BUILD_GDB AND UNIX)
+    add_subdirectory(src/gdb)
+endif()
+
 # CLI tools
 if(TRACESMITH_BUILD_CLI)
     add_subdirectory(cli)