move ADK to main repo, deprecate old package.

[clutchski]

Summary

Move the ADK (Google Agent Development Kit) integration from a separate package (braintrust-adk) into the main braintrust package.

Changes:

• Add braintrust.wrappers.adk module with all ADK tracing functionality
• Add ADK to auto_instrument() - automatically instruments ADK if installed
• Deprecate braintrust-adk package (v0.4.0) - re-exports from main package with deprecation warning
• Add nox test sessions for google-adk (latest and 1.14.1)

Migration for users:

# Old (deprecated):
from braintrust_adk import setup_adk

# New (recommended):
import braintrust
braintrust.auto_instrument()  # ADK traced automatically if installed

# Or manual import:
from braintrust.wrappers.adk import setup_adk

Test plan

• Run nox -s "test_google_adk(latest)" - all tests pass
• Run deprecated package tests in integrations/adk-py - all 37 tests pass
• Verify auto_instrument() detects and instruments ADK when installed

🤖 Generated with Claude Code