This commit introduces a significant number of improvements to the ab-proxy tool:

1.  Go Version Compatibility:
    *   Ensured the project builds and runs correctly with Go 1.22.2.
    *   Updated `go.mod` to specify `go 1.22.2`.
    *   Dependencies were verified to be compatible, and `go.sum` was updated.

2.  Refactoring for Testability:
    *   The main application logic in `ab-proxy.go` was refactored.
    *   Core benchmarking functionality was moved into a `runBenchmark` function.
    *   Global state for options, statistics, and error collection was encapsulated into structs (`Options`, `Stats`, `ErrorCollector`), making the code more modular and testable.

3.  Unit Tests:
    *   Added extensive unit tests in `ab_proxy_test.go`.
    *   These tests cover argument parsing, default value handling, header preparation, proxy configuration logic, URL validation, and the `ErrorCollector` functionality.

4.  Integration Tests:
    *   Introduced mock HTTP target and HTTP proxy servers (`mockservers_test.go`) to simulate real-world scenarios.
    *   Added a comprehensive suite of integration tests in `ab_proxy_integration_test.go`.
    *   These tests execute `ab-proxy` as a subprocess and verify its behavior against the mock servers, covering:
        *   Basic GET requests and statistics reporting.
        *   Custom User-Agent and header propagation.
        *   Client-side timeout functionality.
        *   HTTP proxying.
        *   Handling of target server errors (e.g., HTTP 500).
        *   Error reporting for connection failures (e.g., connection refused) using `--show-errors`.
        *   Functionality of multiple bursts and delays.

5.  Dockerization for Testing:
    *   Added a `Dockerfile` that creates a containerized environment with Go 1.22.2.
    *   The Dockerfile is configured to build the application and run all unit and integration tests.
    *   All tests were confirmed to pass within this Docker environment.

These changes enhance the reliability and maintainability of `ab-proxy` by providing a strong testing foundation and ensuring compatibility with an updated Go version.