Major improvements: rollbacks, testing, docs, and code quality

- Fixed rollback implementation with two-phase approach (remove new, downgrade upgraded)
- Added explicit package tracking (newly_installed vs upgraded)
- Implemented graceful error handling with fail-fast approach
- Added comprehensive test suite (20 tests across 3 test files)
- Created centralized APT command execution module (apt_commands.rs)
- Added configuration system with dry-run, quiet, and APT options
- Reduced code duplication and improved maintainability
- Added extensive documentation (rollbacks.md, rollbacks-not-featured.md, ffi-bridge.md)
- Created configuration usage example
- Updated README with crate usage instructions
- All tests passing, clean compilation, production-ready

docs/ffi-bridge.md

@@ -0,0 +1,51 @@
+# FFI Bridge Documentation
+
+## Overview
+
+The APT Wrapper provides a C++ Foreign Function Interface (FFI) bridge for integration with C++ applications, particularly designed for apt-ostree.
+
+## C++ Integration
+
+### Header File
+
+The bridge requires a C++ header file `apt-wrapper/bridge.h` that defines the C++ side of the interface.
+
+### AptPackage FFI
+
+The `AptPackage` struct can be used across the FFI boundary:
+
+```cpp
+// C++ side
+#include "apt-wrapper/bridge.h"
+
+// Create package from Rust
+AptPackage package = new_ffi("vim", "2:8.1.2269-1ubuntu5", "Vi IMproved", true);
+
+// Access package properties
+std::string name = package.name();
+std::string version = package.version();
+std::string description = package.description();
+bool installed = package.is_installed();
+```
+
+### Rust Side Functions
+
+```rust
+// Rust side - these functions are exposed to C++
+pub fn new_ffi(name: String, version: String, description: String, installed: bool) -> AptPackage;
+pub fn name_ffi(package: &AptPackage) -> &str;
+pub fn version_ffi(package: &AptPackage) -> &str;
+pub fn description_ffi(package: &AptPackage) -> &str;
+pub fn is_installed_ffi(package: &AptPackage) -> bool;
+```
+
+## Usage in C++ Projects
+
+1. Include the generated header file
+2. Link against the Rust library
+3. Use the FFI functions to interact with APT packages
+
+## Dependencies
+
+- `cxx` crate for FFI generation
+- C++ compiler with C++17 support