Add experimental high-speed tunnel engine

[ahmadmjwzk]

This PR adds an experimental tunnel engine intended to fix the slow-speed behavior some users can experience when Intra is enabled.

Problem:
Intra can make the internet much slower while it is running, especially on fast connections. The app may still work correctly, but downloads, uploads, video apps, and speed-sensitive services can feel much slower than they should.

Fix:
This prototype adds a new experimental tunnel engine that keeps Intra’s full protection behavior while allowing much higher network speed in testing.

The existing engine remains the default, so normal builds are not changed.

What this keeps working:

• Normal browsing
• Apps that depend on Intra’s full-tunnel behavior
• Secure DNS handling
• Query history
• Existing VPN setup

What changed:

• Added an experimental high-speed tunnel engine.
• Kept the current engine as the safe default.
• Put the new engine behind an experimental build flag.
• No user-facing setting was added yet.

Validation:

• Browsing works.
• Full-tunnel app behavior worked in tested scenarios.
• DNS query history continued updating.
• VPN stayed connected during high-speed testing.
• Local testing showed much higher speed than the current engine.

Why experimental:
The new engine is promising, but it needs more testing before becoming the default. It should be tested across more phones, Android versions, networks, and apps.

Known areas needing more testing:

• Long-running stability
• Video and social apps
• Games and messaging apps
• Wi-Fi/mobile switching
• Sleep and wake behavior
• Captive portal networks
• Custom DNS servers

Next steps:

1. Test on more devices and networks.
2. Run longer stability tests.
3. Check more apps.
4. Improve cleanup and lifecycle handling.
5. Decide later whether this engine should become the default.

[google-cla]

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[ahmadmjwzk]

I have signed the Google CLA. Could you please re-run the CLA check?