[extensions] Avoid global state in the ADK plugin

[igalshilman]

No description provided.

[Copilot]

Pull request overview

This PR refactors the ADK plugin to eliminate global state by moving plugin state management from class-level dictionaries to per-invocation context extension data. This improves thread safety and prevents state leakage between concurrent invocations.

Key changes:

• Introduced extension data storage in ServerInvocationContext with lifecycle management
• Replaced global _models and _turnstiles dictionaries with context-bound PluginState
• Added automatic cleanup of extension data via auto_close_extension_data context manager

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
python/restate/server_context.py	Adds extension data API (get/set/clear) and auto-cleanup context manager to ServerInvocationContext
python/restate/ext/adk/plugin.py	Refactors RestatePlugin to use context extension data instead of instance-level dictionaries for state management

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Test Results

  7 files  ±0    7 suites  ±0   4m 25s ⏱️ +3s
 49 tests ±0   49 ✅ ±0  0 💤 ±0  0 ❌ ±0 
210 runs  ±0  210 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 021fd74. ± Comparison against base commit 903d148.