feat: support dynamic fee tiers based on volume (#317)

[milah-247]

Description

Implements a dynamic fee tier system where the protocol fee percentage decreases as the total pool stake increases. This encourages participation in larger markets by rewarding high-volume pools with lower fees.

Related Issue

Fixes #317
Depends on #304

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Changes Made

• Added new contract function(s)
• Modified existing function(s)
• Added/updated tests
• Updated documentation

Testing

• All existing tests pass
• Added tests for new functionality
• Tested on local environment
• Manual testing completed

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

N/A

Additional Notes

Files Modified:

File	Change
contracts/predifi-contract/src/lib.rs	Added FeeTier struct, DataKey::FeeTiers, set_fee_tiers(), get_fee_tiers(), calculate_dynamic_fee_bps(), updated claim_winnings()
contracts/predifi-contract/src/integration_test.rs	Fixed pre-existing test failure by whitelisting token in setup_integration()
contracts/predifi-contract/src/test.rs	Fixed pre-existing test: added missing category argument to create_pool() call

New Data Structures:

#[contracttype]
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct FeeTier {
    pub min_stake: i128, // Minimum total stake to qualify for this tier
    pub fee_bps: u32,    // Fee in basis points (e.g. 50 = 0.5%)
}

New Admin Functions:

Function	Description
set_fee_tiers(env, admin, tiers)	Sets the fee tier schedule. Admin only. Tiers must be sorted by min_stake ascending
get_fee_tiers(env)	Returns the current fee tier schedule

Example Fee Tier Configuration:

// Tier 1: Default fee for small pools
FeeTier { min_stake: 0,         fee_bps: 200 } // 2.0%
// Tier 2: Reduced fee for mid-size pools
FeeTier { min_stake: 500_000,   fee_bps: 100 } // 1.0%
// Tier 3: Lowest fee for large pools
FeeTier { min_stake: 1_000_000, fee_bps: 50  } // 0.5%

New Events:

Event	Trigger
FeeTierUpdateEvent	Emitted when admin updates fee tiers
FeeTierAppliedEvent	Emitted on each claim, records which fee tier was applied

Fee Calculation Logic (claim_winnings):

• calculate_dynamic_fee_bps() iterates tiers in ascending order and returns the fee for the highest qualifying tier
• Falls back to config.fee_bps if no tiers are configured, maintaining full backward compatibility
• Fee deducted from gross winnings; net amount transferred to user; fee amount transferred to treasury

Test Results:

test result: ok. 60 passed; 0 failed
test result: ok. 11 passed; 0 failed
Total: 71 tests passed, 0 failed

[vercel]

@milah-247 is attempting to deploy a commit to the shola's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Yunusabdul38]

@milah-247 relove conflict and ci

[Yunusabdul38]

@milah-247 any update on this