feat(insurance-pool): add per-claim caps and cooldown windows

[priscaenoch]

Summary

Closes #10

Adds configurable per-claim payout caps and a per-claimant cooldown to the insurance pool's claim flow (soroban/src/insurance_pool.rs), so a single large claim or a rapid series of claims from the same claimant can no longer drain a pool unchecked.

• PoolInfo gains three new fields:

  • max_claim_amount: i128 — absolute per-claim cap (0 disables it)
  • max_claim_bps: u32 — per-claim cap as a percentage of total_liquidity (0 disables it)
  • claim_cooldown_secs: u64 — minimum seconds between claims from the same claimant on a pool (0 disables it)

  create_pool seeds new pools with protective defaults — 20% of the pool per claim, 1-day cooldown — so pools are safe out of the box without a redeploy, per the issue's note to keep these as tunable parameters with defaults.

• New configure_claim_limits(pool_id, max_claim_amount, max_claim_bps, claim_cooldown_secs) admin-only entrypoint to tune (or disable) these per pool, mirroring the existing set_risk_score/configure_governance pattern already used in this file.

• submit_claim now enforces both caps and the cooldown before recording a claim, reverting with specific messages consistent with this file's existing panic!-based error style (it doesn't use a Result/error-enum elsewhere, so I kept that convention rather than introducing a new one just for this):

  • "claim exceeds maximum claim amount"
  • "claim exceeds maximum claim percentage of pool"
  • "claim cooldown active"

  Cooldown tracking reuses the cooldown_until-timestamp pattern already established in soroban/src/rate_limiter.rs (a new DataKey::ClaimCooldown(Address, String) entry keyed per claimant per pool) rather than introducing separate timing logic, per the approach outlined in the issue thread.

• One pre-existing test (test_fraudulent_claim_slashing) had its stake amount bumped from 8_000 to 10_000 so its claim continues to clear the new default 20% cap — that's the only change to existing code/tests; its actual behavior (fraud slashing) is unchanged.

• Added 8 new tests covering the acceptance criteria: a claim landing exactly on the percentage-cap boundary (allowed), over-cap claims for both the absolute and percentage caps (reverting with the specific error), an admin widening the caps to allow a previously-rejected claim, a non-admin being rejected from configure_claim_limits, a repeat claim within the cooldown reverting, a repeat claim exactly at the cooldown boundary succeeding, and cooldowns being tracked per-claimant rather than globally.

Testing/validation performed

Run locally against a stable Rust toolchain matching CI:

• cargo fmt --all -- --check — passes
• cargo clippy --all-targets --all-features -- -D warnings — passes (no warnings)
• cargo build --release --target wasm32-unknown-unknown — passes
• cargo test (full workspace) — all pass, 525 unit tests in the main lib (up from 517), including the 8 new insurance-pool tests; 0 failures

Issue

#10