Third cluster: NSRunLoop and CADisplayLink move to declarative
`#objc_class` blocks.
Classes declared:
- NSRunLoop → currentRunLoop (class)
- CADisplayLink → displayLinkWithTarget_selector (class),
addToRunLoop_forMode (instance),
targetTimestamp (instance), duration (instance)
The display-link instance is created with the new typed call shape:
link := CADisplayLink.displayLinkWithTarget_selector(plat.gl_view, sel_tick);
plat.display_link = xx link; // keep the *void slot in the
// platform struct for ABI parity
runloop := NSRunLoop.currentRunLoop();
link.addToRunLoop_forMode(runloop, mode_ns);
The `sxTick:` callback's `link: *void` param is cast to
`*CADisplayLink` at function entry so the body's `link.duration()` /
`link.targetTimestamp()` calls type-check.
Two now-redundant `objc_getClass(...)` lookups for CADisplayLink /
NSRunLoop are gone — the class slots come from the declarative
declarations via `__sx_objc_class_init`.
166/166 tests; chess builds clean on macOS / iOS / Android.
2a7c8e0a6f