feat: Implemented Configurable Fee Model (Per-Escrow & Token-Specific Fees) to close #93

[Oluwaseyi89]

Description

This PR introduces a configurable fee model that extends the current flat fee structure to support per-token and per-escrow fee overrides, providing greater flexibility for different assets and use cases.

Key Features

• Maintains existing global fee as default
• Added per-token fee overrides via token_fee_bps mapping
• Added per-escrow fee overrides via escrow_fee_bps mapping
• Clear precedence: escrow override → token override → global default
• All fees bounded to [0, BPS_DENOMINATOR] with validation

New Admin Functions

• set_token_fee(env, token_address, fee_bps) - configure token-specific fees
• set_escrow_fee(env, escrow_id, fee_bps) - configure escrow-specific fees

Events

• FeeUpdated(scope, key, old_fee, new_fee) emitted for all fee changes

Testing

• ✅ Default global fee behavior
• ✅ Token-level override only
• ✅ Escrow-level override only
• ✅ Combined precedence scenarios
• ✅ Invalid fee rejections (>100%)
• All existing tests remain passing

Closes #93

[Oluwaseyi89]

@Cedarich please, review.

[Cedarich]

Please check formatting errors

[Oluwaseyi89]

@Cedarich merge conflicts resolved and fmt errors. Please, review. And I observe you people commited node_modules/

[Oluwaseyi89]

@Cedarich please, review. Clippy errors resolved.

[Cedarich]

@Oluwaseyi89 Boss please fix failing test

[Oluwaseyi89]

@Cedarich bugs causing panic fixed and all tests pass.

[Cedarich]

LGTM