fix: C action buffer lengths, byte-faithful callbacks, runtime finalize

Resolves the 8 gaps in docs/rewrite/notes/review-rv10-codex.md
(final-Z13.md):
- P1 memory safety: the C key-table action (and hovered-link/open-URL
  payloads) could advertise a length larger than the NUL-truncated
  allocation. A counted_bytes helper now passes the full bytes plus a
  trailing NUL with len == byte count, like Zig's backing slices; all
  C pointer+len structs were audited and tested to read exactly len.
- ghostty-bench args follow cli/args.zig (ordered duplicates, empty
  value resets, first bad value errors, parseBool spellings); the C
  benchmark tokenizer uses the ArgIteratorGeneral port.
- OSC 7 derived titles, desktop notifications and OSC 8 hover links
  forward raw bytes to the runtime; GTK converts only for display.
- C diagnostic getter exports original bytes; escaped surrogates report
  Utf8CannotEncodeSurrogateHalf; config float formatters print `nan`.
- Config::finalize_for(AppRuntime): GTK-only finalization (gtk-single-
  instance=detect) and termio's cgroup hooks apply only to the GTK
  runtime, so libghostty keeps `detect` like Zig.

Test Plan:
- cargo test --workspace --no-fail-fast (exit 0)
- cargo test -p ghostty-lib --features test-platform
- just check-wasm (macOS/Windows clippy re-run after the concurrent
  terminal changes land)

crates/ghostty-termio/src/exec.rs

@@ -1066,6 +1066,7 @@ impl Subprocess {
         let pre_info = self.rt_pre_exec_info;
         let post_info = self.rt_post_fork_info;
         let create_scope = self.create_scope.clone();
+        let gtk = ghostty_config::config::app_runtime() == ghostty_config::config::AppRuntime::Gtk;
         let mut cmd = Command {
             path: self.args[0].clone(),
             args: self.args.clone(),
@@ -1081,15 +1082,19 @@ impl Subprocess {
                 let _ = pty::child_pre_exec(master_raw, slave_raw);
                 None
             })),
-            rt_pre_exec: Some(Box::new(move || linux_cgroup_pre_exec(&pre_info))),
-            rt_post_fork: Some(Box::new(move |c: &Command| {
-                let create = |pid, mem, tasks| match &create_scope {
-                    Some(f) => f(pid, mem, tasks),
-                    None => None,
-                };
-                linux_cgroup_post_fork(c, &post_info, create)
-                    .map_err(|_: PostForkError| PostForkError)
-            })),
+            // Zig installs these only when the apprt declares them
+            // (`@hasDecl(apprt.runtime, "pre_exec")`): GTK.
+            rt_pre_exec: gtk.then(|| Box::new(move || linux_cgroup_pre_exec(&pre_info)) as Box<_>),
+            rt_post_fork: gtk.then(|| {
+                Box::new(move |c: &Command| {
+                    let create = |pid, mem, tasks| match &create_scope {
+                        Some(f) => f(pid, mem, tasks),
+                        None => None,
+                    };
+                    linux_cgroup_post_fork(c, &post_info, create)
+                        .map_err(|_: PostForkError| PostForkError)
+                }) as Box<_>
+            }),
             pid: None,
         };