fix(config): match Zig's numeric grammar, NUL handling and diagnostics

Resolves the 6 differential gap groups in docs/rewrite/notes/review-
rv9-codex.md (details in final-Z11.md):
- ghostty_os::zig_fmt ports std.fmt.parseInt/parseUnsigned/parseFloat
  (underscores, 0x/0o/0b prefixes, hex floats, inf/nan) with the Zig std
  tests and replaces every int/float parse in config, keybind
  parameters, ssh-cache and desktop detection.
- Interior NUL no longer panics in font names and ends C strings like
  Zig's backing bytes (fontconfig, C config getters, title actions,
  clipboard callback, relative paths, config-file, shaders, background
  image, GTK CSS).
- GTK new-window arguments are trimmed of ASCII whitespace only.
- Command tokenization uses a port of std.process.ArgIteratorGeneral
  (incl. CR/LF separators) with its std tests.
- UTF-8 validation happens where Zig's field parsers do it, so error
  kinds match (metric modifiers, quick-terminal size, link, ...).

A scripted differential run of 202 fields x ~220 hostile/valid values
against /usr/bin/ghostty (+validate-config and +show-config: exit code,
stdout, stderr) now has zero mismatches besides build-specific defaults
(theme resources path, auto-update-channel, gtk-opengl-debug); it also
surfaced and fixed background-blur failure state, NaN formatting and
NaN/-0 finalize clamps. Regression tests: ghostty-config/tests/
zig_parity.rs.

Test Plan:
- cargo test --workspace --no-fail-fast (3456 passed, exit 0)
- just check-macos (both), just check-windows, just check-wasm

crates/ghostty-font/src/discovery.rs

@@ -162,6 +162,43 @@ mod fc_impl {
 mod tests {
     use super::*;
 
+    #[cfg(font_fontconfig)]
+    #[test]
+    fn interior_nul_in_font_names_ends_the_c_string() {
+        use ghostty_config::config::Config;
+        use ghostty_os::osbytes::os_bytes;
+
+        use crate::fontconfig::Property;
+        let mut config = Config::default();
+        config
+            .parse_field_bytes("font-family", Some(b"monospace\0suffix"))
+            .unwrap();
+        config
+            .parse_field_bytes("font-style", Some(b"Regular\0suffix"))
+            .unwrap();
+        config
+            .parse_field_bytes("font-codepoint-map", Some(b"U+0041=Fam\0ily"))
+            .unwrap();
+        let pat = to_fc_pattern(&Descriptor {
+            family: Some(config.font_family.list[0].clone()),
+            style: config.font_style.name_value().cloned(),
+            ..Descriptor::default()
+        });
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Family, 0).unwrap()),
+            b"monospace"
+        );
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Style, 0).unwrap()),
+            b"Regular"
+        );
+        let pat = to_fc_pattern(&config.font_codepoint_map.map.list[0].descriptor);
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Family, 0).unwrap()),
+            b"Fam"
+        );
+    }
+
     #[cfg(font_fontconfig)]
     #[test]
     fn configured_font_names_reach_fontconfig_as_original_bytes() {

crates/ghostty-font/src/fontconfig.rs

@@ -189,8 +189,10 @@ impl Pattern {
         self.add_string_bytes(prop, v.as_bytes())
     }
 
-    /// [`Pattern::add_string`] for arbitrary bytes (file names).
+    /// [`Pattern::add_string`] for arbitrary bytes (file names). Like Zig's
+    /// sentinel-terminated C string handoff, the value ends at the first NUL.
     pub fn add_string_bytes(&mut self, prop: Property, v: &[u8]) -> bool {
+        let v = v.split(|&b| b == 0).next().unwrap_or(v);
         let Ok(c) = CString::new(v) else {
             return false;
         };