Add per-claim caps and cooldown windows to the insurance pool

[Meshmulla]

Summary

The insurance pool (soroban/src/insurance_pool.rs) is meant to cover losses, but without limits a single large or rapid series of claims could drain it and destabilize the system. Adding per-claim caps and cooldown windows makes payouts safer and more predictable.

What we'd like

• A configurable maximum payout per claim (absolute and/or percentage of pool)
• A cooldown window between claims from the same claimant
• Clear, specific errors when a claim exceeds the cap or is within cooldown

Where to look

• soroban/src/insurance_pool.rs — claim logic
• soroban/src/emergency_fund_recovery.rs — related fund-safety patterns
• soroban/tests/insurance_pool.test.rs — extend coverage
• soroban/src/rate_limiter.rs — reusable cooldown/window mechanics

Acceptance criteria

• Per-claim cap is enforced and admin-configurable
• Cooldown between claims is enforced per claimant
• Over-cap and in-cooldown claims revert with descriptive errors
• Tests cover valid claims, over-cap claims, and cooldown enforcement

Notes

Keep the caps as parameters (with defaults) so they can be tuned via governance without a redeploy.