fix: use Zig's numeric parsing in protocol and escape-sequence parsers

Rust's str::parse accepts and rejects different inputs than Zig's
std.fmt.parseInt/parseFloat (underscores, base prefixes, signs). The
config layer already used the Zig ports; now the protocol parsers do
too (call site -> Zig reference -> status in final-Z12.md):
- zig_fmt moves into the leaf crate ghostty-zigfmt (ghostty-vt cannot
  depend on ghostty-os); ghostty-os re-exports it unchanged.
- ghostty-vt: kitty graphics keys, kitty text sizing, OSC 4/5/10-19
  color indices, hex color components and intensities, OSC 9 sleep and
  progress, OSC 133 exit codes, OSC 3008 fields, kitty color palette.
- ghostty-terminal: tmux layout, format variables and pane tabs.
- ghostty-os: URI ports and %XX decoding; ghostty-bench CLI arguments.
Expected values were cross-checked against the real Zig toolchain.

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

Cargo.toml

@@ -56,6 +56,7 @@ ghostty-font = { path = "crates/ghostty-font" }
 ghostty-renderer = { path = "crates/ghostty-renderer" }
 ghostty-termio = { path = "crates/ghostty-termio" }
 ghostty-os = { path = "crates/ghostty-os" }
+ghostty-zigfmt = { path = "crates/ghostty-zigfmt" }
 ghostty-onig = { path = "crates/ghostty-onig" }
 ghostty-datastruct = { path = "crates/ghostty-datastruct" }
 ghostty-core = { path = "crates/ghostty-core" }