Three-Way Split & Reseller Revenue Sharing (Soroban SDK Compliance)

[GazzyLee]

Summary:

• Implements a three-way split for utility revenue: Main Provider, Reseller, and Platform.
• Adds support for neighborhood "Electricity Resellers" to take a configurable cut of managed drip.
• Each party has independent withdrawal counters for accurate, auditable revenue sharing.
• Refactors contract to fully comply with Soroban SDK constraints (no f32, correct event topics, struct completeness).
• Fixes all previous build errors, duplicate definitions, and type mismatches.
• Cleans up contract and test code for maintainability.

Key Changes:

• New data models: ResellerConfig, ResellerEarnings, ResellerWithdrawn.
• Extended Meter struct and storage keys for reseller logic.
• New/updated contract methods: assign_reseller, remove_reseller, reseller_withdraw, get_reseller_earnings, get_reseller_config.
• All struct initializers and event topics updated for Soroban SDK.
• Removed unsupported summary string methods and fixed all integer/string conversions.
• Duplicate and deprecated code removed.
• All tests and logic now build and pass under Soroban SDK.

How to Review:

• Focus on new/updated contract logic for revenue sharing and withdrawal.
• Review Soroban SDK compliance changes (types, events, struct fields).
• See test coverage for reseller assignment, withdrawal, and error cases.

** Closes #125

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