🧪 Add error testing for CdpConfig::host_isolated_localhost

[undivisible]

This pull request addresses the testing gap for the CdpConfig::host_isolated_localhost function by passing invalid arguments to the function and asserting that they each return the CdpError::InvalidConfig error. The newly added host_isolated_localhost_rejects_invalid_config function validates various edge case states (port 0, empty strings, missing browser_process_id, etc).

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PR created automatically by Jules for task 16820371949676347824 started by @undivisible

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Note

Low Risk
Test-only change; no runtime or CDP connection behavior is modified.

Overview
Adds unit test host_isolated_localhost_rejects_invalid_config so CdpConfig::host_isolated_localhost is covered the same way other localhost builders are for validation failures.

Each case passes bad input (port 0, empty or invalid target_id, browser_process_id 0, or a stale process_generation) and expects CdpError::InvalidConfig, matching the shared localhost_with_isolation checks used by both shared-desktop and host-isolated configs.

^{Reviewed by Cursor Bugbot for commit d2d4e33. Configure here.}

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