[Contracts] Bond: add liquidation entrypoint for fully-slashed/expired bonds with event

[Baskarayelu]

Description

The contract supports slashing (slash/slash_bond) and per-identity withdrawal, but there is no explicit liquidation path that finalizes a bond whose slashed_amount == bonded_amount or whose lock-up has long expired without renewal. The bond is described as the source of truth for liquidation, yet active is only ever set false inside withdraw_bond. We need a dedicated liquidate entrypoint that marks such bonds closed, sweeps residual slashed funds to the treasury, and emits a liquidation event the keeper/indexer can act on.

Requirements and context

• Secure: liquidate(identity) callable by admin/keeper; only valid when fully slashed or expired-and-unrenewed; transfer residual to treasury (after token integration); set active = false.
• Idempotent: re-liquidating an already-liquidated bond reverts cleanly.
• Tested: liquidate fully-slashed bond, expired bond, reject healthy bond, idempotency.
• Documented: add docs/liquidation.md referencing the existing paginated liquidation scanner work.

Suggested execution

• git checkout -b feature/bond-liquidation-entrypoint
• Add liquidate to ours.rs with eligibility checks and event.
• Write eligibility and idempotency tests.
• Add docs docs/liquidation.md.
• Add /// doc comments on eligibility rules.
• Validate only eligible bonds can be liquidated.

Test and commit

• Run cargo test.
• Cover edge cases: partially slashed (reject), expired rolling vs fixed, double-liquidate.
• Include test output and security notes.

Example commit message

feat: add bond liquidation entrypoint for fully-slashed/expired bonds

Guidelines

• Minimum 95% test coverage
• Clear documentation
• Timeframe: 96 hours

[Topmatrixmor2014]

@Topmatrixmor2014 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I am interested in working on this issue and i shall deliver qualitatively and promptly on this

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