docs: add audit report for slash delay & blacklist fix and update readme (#1753) (#1755)

**Motivation:**

The Certora security assessment for the Redistribution Slash Delay
Upgrade (PR #1753, v1.13.0) was completed but is not yet published in
the `/audits` directory alongside the other EigenLayer audit reports.

**Modifications:**

- Added the final Certora report for the slash resolution delay and
duration-vault blacklist fix.

**Result:**

Up to date `/audits` dir; the slash-delay upgrade's audit is now
publicly available.

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Co-authored-by: Nadir Akhtar <9601075+nadir-akhtar@users.noreply.github.com>
Co-authored-by: ELHAJ <124453227+elhajin@users.noreply.github.com>

Author: nadir-akhtar