perf: pause CADisplayLink instead of re-creation (#980)

## 📜 Description

Pause `DisplayLink` instead of re-creating it before any keyboard
movement.

## 💡 Motivation and Context

This is a known fact, that pausing `CADisplayLink` is faster operation
rather than re-creating it and attaching to the thread. I decided to
make some benchamrkes, and it seems like it takes `1ms` for `10` runs:

<img width="516" alt="image"
src="https://github.com/user-attachments/assets/b6bb5c28-bffa-46d0-b499-4855ebb3454f"
/>

I tried to re-run test 40 times, and the function wasn't in a stack
trace - that means that the time was so insignificant. I also measure
function execution:
- pausing: 1.5-2e^-6
- re-creating: 7-10e-6

So roughly speaking this is 5x improvement, but we measure only creating
instances of new object (most likely we don't track what happens
underhood).

Anyway, this is an optimization and I don't think it introduces any
breaking changes, so let's keep it.

## 📢 Changelog

<!-- High level overview of important changes -->
<!-- For example: fixed status bar manipulation; added new types
declarations; -->
<!-- If your changes don't affect one of platform/language below - then
remove this platform/language -->

### iOS

- pause `DisplayLink` instead of re-creating it;

## 🤔 How Has This Been Tested?

Tested via Profiler. Also tested functionality manually and via e2e
tests.

## 📸 Screenshots (if appropriate):

<img width="965" alt="image"
src="https://github.com/user-attachments/assets/395b4511-4195-49e2-84fb-9beef91dfb4f"
/>

## 📝 Checklist

- [x] CI successfully passed
- [x] I added new mocks and corresponding unit-tests if library API was
changed

Author: kirillzyusko

ios/observers/KeyboardMovementObserver.swift

@@ -32,7 +32,7 @@ public class KeyboardMovementObserver: NSObject {
 
   private var _windowsCount: Int = 0
   private var prevKeyboardPosition = 0.0
-  private var displayLink: CADisplayLink?
+  private var displayLink: CADisplayLink!
   private var interactiveKeyboardObserver: NSKeyValueObservation?
   private var isMounted = false
   // state variables
@@ -57,6 +57,18 @@ public class KeyboardMovementObserver: NSObject {
     self.onNotify = onNotify
     self.onRequestAnimation = onRequestAnimation
     self.onCancelAnimation = onCancelAnimation
+
+    super.init()
+
+    displayLink = CADisplayLink(target: self, selector: #selector(updateKeyboardFrame))
+    displayLink.preferredFramesPerSecond = 120 // will fallback to 60 fps for devices without Pro Motion display
+    displayLink.add(to: .main, forMode: .common)
+    displayLink.isPaused = true
+  }
+
+  deinit {
+    displayLink.invalidate()
+    displayLink = nil
   }
 
   @objc public func mount() {
@@ -109,7 +121,7 @@ public class KeyboardMovementObserver: NSObject {
 
   private func keyboardDidMoveInteractively(changeValue: CGPoint) {
     // if we are currently animating keyboard -> we need to ignore values from KVO
-    if displayLink != nil {
+    if !displayLink.isPaused {
       return
     }
     // if keyboard height is not equal to its bounds - we can ignore
@@ -232,18 +244,15 @@ public class KeyboardMovementObserver: NSObject {
     // sometimes `will` events can be called multiple times.
     // To avoid double re-creation of listener we are adding this condition
     // (if active link is present, then no need to re-setup a listener)
-    if displayLink != nil {
+    if !displayLink.isPaused {
       return
     }
 
-    displayLink = CADisplayLink(target: self, selector: #selector(updateKeyboardFrame))
-    displayLink?.preferredFramesPerSecond = 120 // will fallback to 60 fps for devices without Pro Motion display
-    displayLink?.add(to: .main, forMode: .common)
+    displayLink.isPaused = false
   }
 
   @objc func removeKeyboardWatcher() {
-    displayLink?.invalidate()
-    displayLink = nil
+    displayLink.isPaused = true
   }
 
   func initializeAnimation(fromValue: Double, toValue: Double) {