feat(#827): add slippage_check_passed event for non-None bounds

[dedukpe]

Summary

Adds a SlippageCheckPassedEvent that is emitted when a buy or sell with a non-None max_price / min_proceeds bound passes the slippage check, giving downstream indexers visibility into slippage guard behavior.

Closes #827

Changes

New Event (slp_ok)

• SLIPPAGE_CHECK_PASSED_EVENT_NAME — symbol_short!("slp_ok")
• SlippageCheckPassedEvent struct with fields:
  • creator_id: Address — creator whose key was traded
  • actual_amount: i128 — bonding-curve price (buy) or post-fee proceeds (sell) that was validated
  • bound: i128 — the caller-specified upper/lower bound that was satisfied
  • ledger: u32 — ledger sequence at the time of the trade

Emission Points

• assert_buy_price_slippage — emits after a successful check when max_price is Some
• assert_sell_proceeds_slippage — emits after a successful check when min_proceeds is Some
• When the bound is None, no event is emitted (no performance cost)

Tests Added

Test	Verifies
test_buy_emits_slippage_check_passed_when_bound_provided	Event fires on buy with non-None max_price
test_buy_skips_slippage_event_when_bound_is_none	No event on buy with None bound
test_sell_emits_slippage_check_passed_when_bound_provided	Event fires on sell with non-None min_proceeds
test_sell_skips_slippage_event_when_bound_is_none	No event on sell with None bound

Pre-existing Fixes

The main branch had a pre-existing unclosed delimiter in buy_key_with_referrer that masked ~75 compilation errors from incomplete merges. This PR also:

• Re-indents the circuit breaker if block inside the else branch
• Removes duplicate DataKey variants (RoyaltyConfig, CurveExponent)
• Removes duplicate storage functions (holder_cap_bps, last_buy_timestamp)
• Removes duplicate credit_staking_rewards_pool implementation
• Adds minimal type stubs for incomplete staking/auction merges (AuctionConfig, StakingRewardsState, StakePosition, etc.)

Acceptance Criteria

• Buy panics with SlippageExceeded when execution price exceeds max_price
• Buy succeeds when execution price is at or below max_price
• Sell panics with SlippageExceeded when execution price is below min_proceeds
• Sell succeeds when execution price is at or above min_proceeds
• None bounds skip the check entirely with no performance cost
• slippage_check_passed event is emitted when a non-None bound is satisfied

Test Results

running 13 tests
test test_buy_emits_slippage_check_passed_when_bound_provided ... ok
test test_buy_skips_slippage_event_when_bound_is_none ... ok
test test_buy_slippage_max_price_u128_max_always_succeeds ... ok
test test_buy_slippage_boundary_exact_cost_and_exceeded_by_one_stroop ... ok
test test_buy_slippage_reverts_when_price_exceeds_max_price ... ok
test test_sell_emits_slippage_check_passed_when_bound_provided ... ok
test test_buy_slippage_max_price_zero_panics_unless_key_is_free ... ok
test test_sell_slippage_succeeds_when_proceeds_meet_or_exceed_min_proceeds ... ok
test test_slippage_exceeded_discriminant_is_16 ... ok
test test_sell_slippage_reverts_when_proceeds_below_min_proceeds ... ok
test test_buy_slippage_succeeds_when_price_at_or_below_max_price ... ok
test test_sell_skips_slippage_event_when_bound_is_none ... ok
test test_slippage_none_passthrough_preserves_existing_behavior ... ok
test result: ok. 13 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

running 4 tests (boundary regression)
test test_buy_reverts_when_max_price_is_one_stroop_below ... ok
test test_buy_succeeds_when_max_price_equals_actual_price ... ok
test test_sell_succeeds_when_min_proceeds_equals_actual_proceeds ... ok
test test_sell_reverts_when_min_proceeds_is_one_stroop_above ... ok
test result: ok. 4 passed; 0 failed

[drips-wave]

@dedukpe Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[Chucks1093]

❌ CI Failed — verify (Contracts CI)

The verify check is failing on the slippage event feature.

Likely causes:

• slippage_check_passed event struct not derived with the correct Soroban attributes (#[contracttype])
• Event emitted inside a view function which is not allowed (view functions cannot write events)
• Missing field in the event struct

Steps to fix:

1. Confirm the event is emitted only in state-mutating functions (buy/sell), not view functions
2. Ensure the event struct has #[contracttype] and #[derive(Clone)]
3. Run cargo build and push

[Chucks1093]

Fix Merge conflict