feat: port GTK version fallbacks, helpgen, bench modes, CLI leftovers

- apprt-gtk: Ghostty's runtime+build-time version gating (at_least)
  with cargo features adw_1_3/adw_1_4/adw_1_5/gtk_4_16 (default on) and
  the fallbacks for older libraries: MessageDialog (adw < 1.5),
  clipboard dialog without SwitchRow, pre-Banner debug warning and
  child-exited widgets, the old about dialog, GTK 4.16 CSS error source
  bytes. The minimum stays GTK 4.14 / libadwaita 1.5 (Ghostty's floor).
  The root build links with -z lazy so version-gated symbols don't keep
  older libraries from loading.
- ghostty-helpgen (port of helpgen.zig) generates CLI action help and
  keybinding action docs from doc comments at build time, replacing the
  checked-in help/*.txt; +help and +list-actions --docs stay
  byte-identical to Ghostty 1.3.1.
- ghostty-bench: libc wcwidth mode and separate simd/table and
  uucode/table code paths like Zig.
- ghostty-cli: Windows branches of edit-config, list-colors,
  list-keybinds and boo; ssh-cache DiskCache flock locking (no-op on
  Windows, as in Zig) with an exclusivity test.

Test Plan:
- cargo test --workspace
- diff <(cargo run -q -- +list-actions --docs) \
  <(ghostty +list-actions --docs)

crates/ghostty-apprt-gtk/src/class/surface_child_exited.rs

@@ -1,26 +1,41 @@
 //! Port of apprt/gtk/class/surface_child_exited.zig.
 //!
-//! Child exited overlay based on `adw.Banner` (Adwaita 1.3+; the crate
-//! requires 1.5 so the Zig `SurfaceChildExitedNoop` fallback is omitted).
-//! Emits `close-request` when the banner button is clicked.
+//! Child exited overlay based on `adw.Banner` (Adwaita 1.3+, the `adw_1_3`
+//! build level; emits `close-request` when the banner button is clicked).
+//! Without it Zig compiles `SurfaceChildExitedNoop`, an empty widget that
+//! immediately asks to be closed (`NOOP == true`); so does this port.
 
+#[cfg(feature = "adw_1_3")]
 use std::sync::OnceLock;
 
+#[cfg(feature = "adw_1_3")]
 use adw::{prelude::*, subclass::prelude::*};
 use ghostty_apprt::surface::ChildExited;
-use gtk::{glib, glib::subclass::Signal};
+use gtk::glib;
+#[cfg(feature = "adw_1_3")]
+use gtk::glib::subclass::Signal;
+#[cfg(not(feature = "adw_1_3"))]
+use gtk::prelude::*;
 
 /// Boxed wrapper so `ChildExited` can be a GObject property.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, glib::Boxed)]
 #[boxed_type(name = "GhosttyChildExited", nullable)]
 pub struct ChildExitedBoxed(pub ChildExited);
 
+#[cfg(feature = "adw_1_3")]
 glib::wrapper! {
     pub struct SurfaceChildExited(ObjectSubclass<imp::SurfaceChildExited>)
         @extends adw::Bin, gtk::Widget,
         @implements gtk::Accessible, gtk::Buildable, gtk::ConstraintTarget;
 }
 
+#[cfg(not(feature = "adw_1_3"))]
+glib::wrapper! {
+    pub struct SurfaceChildExited(ObjectSubclass<imp::SurfaceChildExited>)
+        @extends gtk::Widget,
+        @implements gtk::Accessible, gtk::Buildable, gtk::ConstraintTarget;
+}
+
 impl Default for SurfaceChildExited {
     fn default() -> Self {
         Self::new()
@@ -28,16 +43,27 @@ impl Default for SurfaceChildExited {
 }
 
 impl SurfaceChildExited {
+    /// Can be detected at compile time (Zig: `pub const noop = true`).
+    pub const NOOP: bool = !cfg!(feature = "adw_1_3");
+
     #[must_use]
     pub fn new() -> Self {
         glib::Object::new()
     }
 
     /// Set the child exited data (Zig: `setData`).
+    #[cfg(feature = "adw_1_3")]
     pub fn set_child_exited(&self, data: Option<&ChildExited>) {
         self.set_data(data.map(|d| ChildExitedBoxed(*d)));
     }
 
+    /// Set the child exited data (Zig: `setData`); the noop widget just asks
+    /// to be closed.
+    #[cfg(not(feature = "adw_1_3"))]
+    pub fn set_child_exited(&self, _data: Option<&ChildExited>) {
+        self.emit_by_name::<()>("close-request", &[]);
+    }
+
     pub fn connect_close_request<F: Fn(&Self) + 'static>(&self, f: F) -> glib::SignalHandlerId {
         self.connect_closure(
             "close-request",
@@ -47,6 +73,7 @@ impl SurfaceChildExited {
     }
 }
 
+#[cfg(feature = "adw_1_3")]
 mod imp {
     use std::cell::RefCell;
 
@@ -141,3 +168,31 @@ mod imp {
     impl WidgetImpl for SurfaceChildExited {}
     impl BinImpl for SurfaceChildExited {}
 }
+
+/// Empty widget that does nothing if we don't have a new enough Adwaita
+/// version to support the child exited banner.
+#[cfg(not(feature = "adw_1_3"))]
+mod imp {
+    use std::sync::OnceLock;
+
+    use gtk::{glib, glib::subclass::Signal, subclass::prelude::*};
+
+    #[derive(Default)]
+    pub struct SurfaceChildExited;
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for SurfaceChildExited {
+        const NAME: &'static str = "GhosttySurfaceChildExited";
+        type Type = super::SurfaceChildExited;
+        type ParentType = gtk::Widget;
+    }
+
+    impl ObjectImpl for SurfaceChildExited {
+        fn signals() -> &'static [Signal] {
+            static SIGNALS: OnceLock<Vec<Signal>> = OnceLock::new();
+            SIGNALS.get_or_init(|| vec![Signal::builder("close-request").build()])
+        }
+    }
+
+    impl WidgetImpl for SurfaceChildExited {}
+}