[objective_c] FFI is slower than method channels in some cases

I am building a package to get IANA timezone ID and list of supported timezones using native binding.
And comparing my package to other package that uses method channels it seems slower in some situations

https://pub.dev/packages/system_timezone
https://pub.dev/packages/flutter_timezone

***Speed numbers in `μs`***

**Here are some benchmarks on MacOS App in release mode:**

**Get current time zone ID**

| run number | r1 | r2 | r3 | r4 | r5 | r6 |
| -------------- | --- | --- | --- | --- | --- | --- |
| FFI | 748 | 21 | 9 | 14 | 7 | 4 |
| Method Channel | 448 | 86 | 100 | 279 | 66 | 64 |

I ran the benchmark multiple times, what I have observed:
- FFI first run is way worse than next runs
- FFI first run could be worse than method Channel

**Get list of supported timezones**

| run number | r1 | r2 | r3 | r4 | r5 | r6 |
| -------------- | ---- | ---- | ---- | ---- | --- | --- |
| FFI | 5234 | 1371 | 1256 | 1117 | 869 | 916 |
| Method Channel | 579 | 308 | 4626 | 320 | 269 | 261 |

I ran the benchmark multiple, what I have observed:
- FFI is consistency way worse than method channels
- FFI first run is way worse than next runs
- Converting `NSArray` to `List` is the cause of slowness

After the benchmarks :
1- Is there a way to speed up first run ?
2- Is there more efficient way to convert `NSArray` to `List` ?

Benchmark repo:
https://github.com/HosamHasanRamadan/native-vs-method-channel

Flutter doctor

```console
[✓] Flutter (Channel stable, 3.22.3, on macOS 14.3.1 23D60 darwin-arm64, locale en-EG)

• Flutter version 3.22.3 on channel stable at /Users/hosamhasan/fvm/versions/stable

• Upstream repository https://github.com/flutter/flutter.git

• Framework revision b0850beeb2 (7 days ago), 2024-07-16 21:43:41 -0700

• Engine revision 235db911ba

• Dart version 3.4.4

• DevTools version 2.34.3

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)

• Android SDK at /Users/hosamhasan/Library/Android/sdk

• Platform android-34, build-tools 34.0.0

• ANDROID_HOME = /Users/hosamhasan/Library/Android/sdk

• Java binary at: /Users/hosamhasan/Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java

• Java version OpenJDK Runtime Environment (build 17.0.7+0-17.0.7b1000.6-10550314)

• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.2)

• Xcode at /Applications/Xcode-15.2.0.app/Contents/Developer

• Build 15C500b

• CocoaPods version 1.15.2

[✓] Chrome - develop for the web

• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.1)

• Android Studio at /Users/hosamhasan/Applications/Android Studio.app/Contents

• Flutter plugin can be installed from:

🔨 https://plugins.jetbrains.com/plugin/9212-flutter

• Dart plugin can be installed from:

🔨 https://plugins.jetbrains.com/plugin/6351-dart

• Java version OpenJDK Runtime Environment (build 17.0.7+0-17.0.7b1000.6-10550314)

[✓] IntelliJ IDEA Community Edition (version 2023.3.2)

• IntelliJ at /Users/hosamhasan/Applications/IntelliJ IDEA Community Edition.app

• Flutter plugin can be installed from:

🔨 https://plugins.jetbrains.com/plugin/9212-flutter

• Dart plugin version 233.14888

[✓] VS Code (version 1.91.1)

• VS Code at /Applications/Visual Studio Code.app/Contents

• Flutter extension version 3.93.20240702

[✓] Connected device (3 available)

• macOS (desktop) • macos • darwin-arm64 • macOS 14.3.1 23D60 darwin-arm64

• Mac Designed for iPad (desktop) • mac-designed-for-ipad • darwin • macOS 14.3.1 23D60 darwin-arm64

• Chrome (web) • chrome • web-javascript • Google Chrome 126.0.6478.183

[✓] Network resources

• All expected network resources are available.

• No issues found!
```

Start with the linked native-vs-method-channel benchmark repository and reproduce the reported macOS release-mode measurements. Inspect the NSArray-to-List conversion and first-call behavior; done would mean identifying a supported optimization and documenting benchmark results that demonstrate its effect.

Written by the indexing model from the issue text.