Allow using GameAnalytics in Unity Editor

[Gogoshika-ga]

Enable GameAnalytics to run in Unity Editor Play Mode.

Why

Editor-only testing is currently limited, which slows integration/debugging.

Scope

• Add opt-in support for running GA in Editor Play Mode.
• Support init/session/events in Editor mode.
• Document behavior and limitations.

Acceptance Criteria

• GA initializes in Editor Play Mode when enabled.
• Core events work in Editor mode.
• No runtime behavior change when disabled.
• Docs updated.