feat: Added active scene's name to unity context

[bitsandfoxes]

Relates to #2073
Adds the active scene's name to the Unity context.

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📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

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[Copilot]

Pull Request Overview

This PR adds support for reporting the active scene's name in the Unity context to help diagnose issues related to scene loading.

• Updated tests to verify the new ActiveSceneName property in Sentry contexts.
• Modified protocol serialization/deserialization and integration to include ActiveSceneName.
• Adjusted the scene manager interface and fake implementation to support retrieving the active scene name.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/Sentry.Unity.Tests/UnityEventScopeTests.cs	Added assertions to verify the active scene's name is included in the Unity context.
test/Sentry.Unity.Tests/SceneManagerIntegrationTests.cs	Changed FakeSceneManager access level and added GetActiveScene method.
test/Sentry.Unity.Tests/Protocol/UnityTests.cs	Updated tests to check serialization and cloning of ActiveSceneName.
src/Sentry.Unity/Protocol/Unity.cs	Introduced the ActiveSceneName property and updated JSON serialization/deserialization.
src/Sentry.Unity/Integrations/UnityScopeIntegration.cs	Made the scene manager dependency optional and updated scope configuration.
src/Sentry.Unity/Integrations/ISceneManager.cs	Added GetActiveScene to the interface and its adapter.
CHANGELOG.md	Documented the feature addition for reporting the active scene's name.

Comments suppressed due to low confidence (1)

test/Sentry.Unity.Tests/UnityEventScopeTests.cs:162

• [nitpick] There is an inconsistency in casing: here the scene name is accessed as 'name' while in other tests it is referred to as 'Name'. Consider standardizing the casing for improved clarity and consistency.

Assert.AreEqual(SceneManager.GetActiveScene().name, unityContext.ActiveSceneName);