[php-src] PR #23941: Rfc io terminal

Pull Request: https://github.com/php/php-src/pull/23941 Author: prateekbhujel Draft implementation for the proposed PHP 8.7 Io\Terminal RFC. The proposal provides a small native terminal API in ext/standard for cross-platform operations that are not reliably implementable in userland: - native terminal dimensions - raw mode with explicit/restorable ownership - normalized key input - hidden input The API uses Time\Duration for timeout values, following Io\Poll. Reference implementation and prior ecosystem experience: https://github.com/prateekbhujel/php-terminal The formal RFC Wiki page is pending RFC Wiki karma and will be linked here once published. This PR is intentionally a draft while the API is under RFC review. The core implementation is intentionally smaller than ext-terminal's 1.x surface. In particular, it does not include compatibility aliases, convenience APIs, or COLUMNS/LINES environment fallback for terminal dimensions. Tests include the core API surface and regression coverage for mode ownership and input handling.