[Windows port PR3] refactor: replace RawFd/AsyncFile, introduce platform-split PTY backend (#4722)

* refactor: replace RawFd with i32 in debug_to_file

Replace the Unix-specific RawFd type with plain i32 in the debug_to_file
infrastructure. This removes the last RawFd usage from the cross-crate
debug logging API, making it platform-independent.

* refactor: cross-platform PTY abstraction with AsyncFd

Replace portable-pty with native openpty and introduce a platform-split
architecture for PTY operations:

- os_input_output_unix.rs: UnixPtyBackend with native openpty, AsyncFd-based
  epoll reader (no spawn_blocking per pane), signal handling via nix
- os_input_output_windows.rs: WindowsPtyBackend stubs (unimplemented)
- os_input_output.rs: shared ServerOsApi trait, ServerOsInputOutput composes
  PtyBackendImpl, build_command() extracts TerminalAction→RunCommand logic

Key changes:
- AsyncFd<File> replaces both tokio::fs::File (upstream) and spawn_blocking
  SyncReadAsyncReader (previous port) for zero-overhead epoll PTY reads
- orig_termios restored: openpty(None, &orig_termios) passes parent's VERASE
- ServerOsApi returns Box<dyn AsyncReader> instead of Box<dyn Read + Send>
- TerminalBytes::new takes Box<dyn AsyncReader> directly
- NullAsyncReader replaces std::io::empty() for held panes
- Platform modules gated with #[cfg(not(windows))] / #[cfg(windows)]
- Removed portable-pty dependency, restored close_fds
- Added tokio "net" feature for AsyncFd

---------

Co-authored-by: divens <divens.dev@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 1f1fe5b9..93fd75e2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -99,7 +99,7 @@ strum_macros = { version = "0.27.2", default-features = false }
 suggest = { version = "0.4.0", default-features = false }
 tempfile = { version = "3.2.0", default-features = false }
 termwiz = { version = "0.23.2", default-features = false }
-tokio = { version = "1.40", default-features = false, features = ["fs", "rt-multi-thread", "macros", "time", "process", "signal", "io-util", "io-std"] }
+tokio = { version = "1.40", default-features = false, features = ["fs", "rt-multi-thread", "macros", "time", "process", "signal", "io-util", "io-std", "net"] }
 thiserror = { version = "1.0.40", default-features = false }
 tokio-util = { version = "0.7.15" }
 unicode-width = { version = "0.1.8", default-features = false }