fix: reject extending expired pauses

[ayaanoncrypto]

Summary

• Prevent SuperchainConfig.extend() from re-activating an expired pause.
• • Require the identifier to remain actively paused before extending it.
• • Add a regression test covering the expired-pause path.
    Closes bug(SuperchainConfig): extend() can re-activate an expired pause, bypassing Stage 1 requirement #391

Validation

• git diff --check
• • Foundry tests were unavailable in the sandbox because forge is not installed.

[cb-heimdall]

🟡 Heimdall Review Status

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