Implement comprehensive event indexing schema with structured topics and versioning

[AugistineCreates]

This pr closes #167

This pull request redesigns the smart contract event emission system and implements a corresponding versioned event indexing and decoding framework within the SDK. The redesign replaces basic, ad-hoc event logs with structured, multi-topic payloads containing critical block and transaction metadata, ensuring robust off-chain event tracking.

Key Changes

Smart Contract (Rust)

• Centralized event names inside a new EventName enum with explicit conversion to symbols.
• Implemented a versioned emit_event schema helper in contracts/token/src/events.rs.
• Structured event topics to always emit: (ContractSymbol, EventName, Version, LedgerSeq, Timestamp, TxHash).
• Updated contracts/token/src/lib.rs and all emission entry points to use the new standardized structure.

SDK (TypeScript)

• Defined the versioned schema interfaces EventHeader and DecodedEvent matching the contract topics.
• Added version-aware decodeEvent and decodeDiagnosticEvent methods to deserialize RPC and transaction simulation events.
• Added a subscribeEvents handler supporting real-time event polling and client notifications.
• Created mock unit tests verifying decoding accuracy of the versioned schema parameters.

[drips-wave]

@AugistineCreates 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