feat: add graduated bonding curve with supply milestones (#829)

[ayomustap]

Summary

Implements a graduated bonding curve (issue #829): a configurable pricing schedule where the bonding curve exponent switches at configurable supply milestones, allowing creators to steepen price growth as supply grows.

Closes #829

What changed

Graduated curve feature

• set_graduated_curve(env, creator, milestones) — a creator-authorized entrypoint that configures the curve as a list of (supply_threshold, exponent) milestone pairs.
  • Requires the key creator's auth.
  • Requires the creator to be registered.
  • Panics with CurveConfigError::CurveAlreadyActive if any keys have already been sold (read_creator_supply != 0), enforcing that the curve must be set before sales start.
  • Validates exponents are in 1..=5 (InvalidExponent).
  • Validates milestones are in strictly ascending supply-threshold order (InvalidMilestoneOrder).
  • Rejects an empty milestone list (EmptyMilestones).
  • Rejects an unregistered creator (NotRegistered).
• get_graduated_curve(env, creator) — read-only view; returns the configured milestones or an empty vector.
• Pricing integration — compute_bonding_curve_price now takes the graduated curve into account (highest precedence): it selects the exponent for the current supply via graduated_exponent_for_supply (using the last milestone whose threshold <= supply, otherwise the base exponent 1) before falling back to the existing CurveExponent/preset path.
• CurveConfigError — a new error enum because ContractError was already at Soroban's 50-variant cap. Variants are appended at the end of their enum to preserve ABI discriminants.
• Event — graduated_curve_configured (GRADUATED_CURVE_CONFIGURED_EVENT_NAME) emitted with payload GraduatedCurveConfiguredEvent { creator, milestones, ledger }. Event fields are appended (not reordered) for schema stability.
• Storage — DataKey::GraduatedCurve(Address) variant with a graduated_curve(creator) storage helper.

Tests

• Added creator-keys/src/test_graduated_curve.rs with acceptance tests covering:
  • Configuration by the creator and successful milestone-based price stepping.
  • CurveAlreadyActive panic when configuration is attempted after a sale has occurred (test sets a high circuit-breaker threshold before buying so supply becomes > 0).
  • Validation failures: invalid exponent, non-ascending milestones, empty milestones.
  • get_graduated_curve view + the graduated_curve_configured event emission.
  • The graduated-curve price override vs. the base curve.

Build/completeness repair (required to build & test the feature)

The base branch (f251b81) did not compile — it had an unclosed delimiter plus many pre-existing compile errors from a corrupted merge. These had to be repaired for the feature to build and be validated without regressions:

• Closed the unclosed brace in the buy_key_with_referrer circuit-breaker block (root cause of the unclosed delimiter).
• Restored the threshold_pct read (unwrap_or(30)) in the circuit-breaker logic.
• Removed duplicated definitions: FEE_COLLECTED_EVENT_NAME/LOCKUP_BLOCKED_EVENT_NAME and their topic/event types, duplicate RoyaltyConfig/CurveExponent DataKey variants, duplicate holder_cap_bps/last_buy_timestamp storage helpers, and the first duplicate credit_staking_rewards_pool.
• Added missing items: ContractError::GlobalTradingHalted/FreezeQuantityExceedsBalance, several DataKey variants, structs (StakingKey, StakePosition, StakingRewardsState, StakeExit, StakeRewardClaim, AuctionConfig), storage helpers, AuctionPurchaseEvent, and the StakingKey import.
• Reconciles the staking rewards pool storage to consistently use StakingRewardsState between fee crediting (credit_staking_rewards_pool) and the staking entrypoints, which previously wrote/read conflicting types to the same key.
• Added use soroban_sdk::testutils::Ledger to tests/launch_penalty.rs (a pre-existing compile fix unrelated to the feature).

Verification

• cargo build -p creator-keys — compiles (only a pre-existing final_proceeds unused-assignment warning remains, untouched/out of scope).
• cargo test -p creator-keys --lib — 134 passed, 0 failed, including the new test_graduated_curve tests and the previously-failing staking lifecycle test.

Note on remaining pre-existing breakage

Some integration tests under creator-keys/tests/ (co_creator_removal, prelaunch_auction, auction_bonding_curve_transition, staking_reward_claim) still fail to compile because they reference features (e.g. remove_co_creator, configure_auction, get_stake_unlock_ledger, and related event types) that were never implemented/merged into lib.rs in the base. These are pre-existing, out of scope for this issue, and were already non-compiling at the baseline.

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[Chucks1093]

Fix MC

[ayomustap]

@Chucks1093 fixed