feat(terminal): port render state, highlights and the formatter

- render.rs ports render.zig: RenderState, the per-frame snapshot the
  renderer consumes (rows, cells, styles, graphemes, selection,
  highlights, cursor, colors), updated incrementally with Zig's full
  redraw triggers and per-page/per-row dirty tracking. Cells are stored
  struct-of-arrays; use the accessors.
- highlight.rs ports highlight.zig (untracked, tracked, flattened).
- formatter.rs ports formatter.zig: plain, VT and HTML output for
  terminal, screen, page list and page, with selection, rectangle,
  unwrap, trim, palette, codepoint maps, hyperlinks and pin/point maps.
  Screen's test dump helpers now delegate to it.

Cargo.toml also picks up dependencies for the kitty graphics and search
modules that are being ported concurrently.

Test Plan:
- cargo test -p ghostty-terminal --lib (1243 passed; formatter 100/100,
  render 15/15 Zig tests)

crates/ghostty-terminal/src/formatter/tests/mod.rs

@@ -0,0 +1,53 @@
+//! Ported formatter.zig tests, split by Zig source line range:
+//! p1 = "Page plain ..." (Zig lines 1580-3287), p2 = "Page VT ...", "PageList ..."
+//! and "TerminalFormatter ..." (3288-4458), p3 = "Screen ...", "Terminal vt ...",
+//! "Page html ..." up to "Page VT style reset properly closes styles"
+//! (4459-5617), p4 = "Page codepoint_map ..." onwards (5618-end).
+#![allow(dead_code, clippy::needless_range_loop)]
+
+use super::*;
+use crate::{
+    page::Page,
+    page_list::Pin,
+    point::{Coordinate, Point},
+    terminal::{Options as TermOptions, Terminal},
+};
+
+mod p1;
+mod p2;
+mod p3;
+mod p4;
+
+/// Zig `Terminal.init(alloc, .{ .cols, .rows })`.
+pub(super) fn term(cols: u16, rows: u16) -> Terminal {
+    Terminal::new(TermOptions::new(cols, rows)).unwrap()
+}
+
+/// Zig `var s = t.vtStream(); try s.nextSlice(bytes)` (fresh stream per call;
+/// use `t.vt_stream()` directly if parser state must persist).
+pub(super) fn feed(t: &mut Terminal, bytes: &[u8]) {
+    let mut s = t.vt_stream();
+    s.next_slice(bytes).unwrap();
+}
+
+/// Zig `&pages.pages.last.?.data`.
+pub(super) fn last_page(t: &Terminal) -> &Page {
+    let pages = &t.screen().pages;
+    &pages.node(pages.last.unwrap()).unwrap().data
+}
+
+/// Zig `&pages.pages.first.?.data`.
+pub(super) fn first_page(t: &Terminal) -> &Page {
+    let pages = &t.screen().pages;
+    &pages.node(pages.first.unwrap()).unwrap().data
+}
+
+/// Zig `pages.pages.first.?.data.capacity.rows`.
+pub(super) fn first_page_rows(t: &Terminal) -> u16 {
+    first_page(t).capacity.rows
+}
+
+/// Format a whole `PageFormatter` into a string, returning the output.
+pub(super) fn fmt_str(f: PageFormatter<'_>) -> String {
+    f.format_string().unwrap()
+}