feat: emit distinct emergency withdraw event

[silentgeckoaudit3801]

Fixes #1140.

This PR adds a machine-distinguishable EmergencyWithdraw event for the contracts/lending_pool/src/lib.rs::emergency_withdraw path while leaving normal Withdraw emission and fund-movement mechanics unchanged.

Changes:

• defines events::emergency_withdraw in contracts/lending_pool/src/events.rs
• emits it only after a successful emergency redemption
• adds a focused test that verifies the emergency path publishes the distinct event

Validation: static GitHub API/source inspection only; local Soroban/Rust tests were not run in this environment to avoid installing or executing additional toolchains.

[ogazboiz]

this one is still a real gap, main's emergency_withdraw emits no distinct event, so the approach is right. but the branch is based on the old function signature:

1. rebase onto main and adapt to the new emergency_withdraw(..., min_assets_out) signature (it now forwards to redeem_shares with min_assets_out).
2. update the test's emergency_withdraw call accordingly.
3. consider including the withdrawn asset amount in the event data alongside shares_burned, for parity with the regular Withdraw event.

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