lib-vt: move scrollback limits to terminal_set

Terminal construction previously accepted GhosttyTerminalOptions with
dimensions and one scrollback byte limit. Remove the options struct from
the ABI and make ghostty_terminal_new accept columns and rows directly.

Add byte and line limit options to ghostty_terminal_set and forward them
to the runtime Terminal setters. NULL removes a limit, while zero bytes
disables scrollback. Update type metadata, tests, and all API examples.

example/cpp-vt-stream/src/main.cpp

@@ -6,12 +6,7 @@
 int main() {
   // Create a terminal
   GhosttyTerminal terminal;
-  GhosttyTerminalOptions opts = {
-    .cols = 80,
-    .rows = 24,
-    .max_scrollback = 0,
-  };
-  GhosttyResult result = ghostty_terminal_new(nullptr, &terminal, opts);
+  GhosttyResult result = ghostty_terminal_new(nullptr, &terminal, 80, 24);
   assert(result == GHOSTTY_SUCCESS);
 
   // Feed VT data into the terminal