feat: Add mitmproxy-based HTTP caching for testing (do not merge)

[devin-ai-integration]

Description

This PR adds a new mitmproxy-based HTTP caching mechanism for testing, which operates at the OS level by intercepting HTTP requests through environment variables. This approach provides several advantages over the existing requests-cache implementation:

• Compatible with Python 3.12
• Works with any HTTP client library, not just requests
• Can support future Docker-based testing scenarios
• Provides foundation for Java connector testing support

Implementation Details

• Added new airbyte_cdk.testing.proxy_cache package with mitmproxy addon
• Created two pytest fixtures:
  • mitmproxy_auto: Session-scoped, auto-use fixture for global caching
  • mitmproxy_cache: Manual fixture for explicit caching control
• Added mitmproxy as dev dependency and under new 'testing' extras
• Includes basic test coverage demonstrating caching functionality

Testing

• Added unit test verifying cache behavior
• All type checks and linting pass
• Manually verified with example HTTP requests

Notes

• Existing requests-cache implementation remains unchanged
• This is a new feature that will enable gradual migration path

Link to Devin run: https://app.devin.ai/sessions/1afeef8bcd2c44c5ab4f09600e8ec30f

[devin-ai-integration]

🤖 Devin AI Engineer

Original prompt from Aaron:

@Devin - Create a PR that implements just the CDK-side of this solution: <https://chatgpt.com/share/679d02a0-0a78-8004-91bc-ddb27c24a1de>
The goal is to create http caching capabilities to significantly speed up connector rests and reduce flakiness.

When this is ready, I'll ask a different Devin to create the connector-side.

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add "(aside)" to your comment to have me ignore it.
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[devin-ai-integration]

Closing due to inactivity.