fix(unity): compile WebGL players without MQTTnet

[ChiragAgg5k]

MQTTnet.dll is left out of WebGL players, but Push imported it on every platform, so WebGL builds failed to compile.

#if !UNITY_WEBGL || UNITY_EDITOR
using MQTTnet;
// ...
    public class Push : MonoBehaviour { /* MQTT implementation */ }
#else
    public class Push : MonoBehaviour
    {
        // same public API; Subscribe fails with PlatformNotSupportedException("Push is not supported on WebGL")
    }
#endif

Client imports System.Text.Json on every platform, but it and its four managed dependencies were also left out of WebGL, so they are now enabled there. MQTTnet.dll stays off WebGL.

Test: testUnityImportsPluginsLeftOutOfWebglOnlyOffWebgl fails on main (Push.cs imports mqttnet, and Client.cs imports system.text.json with only the guard). The generated Push.cs compiles with UNITY_WEBGL defined. GenerationTest passes (110 tests).

Closes #2060

[hansi-codes]

🟢 Tier S · Ready to merge

The WebGL-specific implementation preserves the Push API, the plugin metadata aligns with the guarded code, and the generation test covers the new platform boundary.

The Unity templates now conditionally exclude the MQTT-backed Push implementation from WebGL players and provide a Push stub whose subscribe methods return PlatformNotSupportedException. The System.Text.Json assemblies and their managed dependencies are enabled for WebGL, and a generation test checks plugin imports against platform availability.

Verdict	New comments	Fixed	Still open
✅ Approved	0	0	0

📂 Walkthrough · 3

File	Change
templates/unity/Assets/Runtime/Push.cs.twig	Guards MQTT imports and implementation off WebGL players and adds the unsupported Push implementation.
templates/unity/Assets/Runtime/Core/Plugins/*.dll.meta	Enables the System.Text.Json runtime and managed dependencies for WebGL while leaving MQTTnet excluded.
tests/generation/GenerationTest.php	Adds coverage for imports of plugins excluded from WebGL players.

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[hansi-codes]

🟢 Tier S · Looks good to merge. Summary