Add instrumentation to verify AltDA code paths for upcoming EigenDA integration

[miguelCyclone]

Description
This PR adds temporary instrumentation in op-e2e/system/setup.go to identify which system tests enter the AltDA initialization path.

Changes

• Set an unreachable DA server URL to force failures during just tests (local results were inconclusive).
• Added a temporary panic inside the AltDA setup block to ensure the code path is executed (local runs did not trigger it).

Motivation

• Opening this PR to run CI and confirm which tests actually reach the AltDA path.

Purpose

• We need CI visibility to determine whether any Espresso tests rely on op-e2e’s FakeDA before introducing the EigenDA toggle and integration.

Notes

• No functional changes; diagnostics only
• Temporary instrumentation to be removed once coverage is confirmed

Let me know if you prefer a different approach or additional instrumentation.

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