feat: add isTerminalTransactionStatus helper

[shoaib050326]

What does this PR do?

Adds a public isTerminalTransactionStatus(status: TransactionStatus): boolean helper, documents the set of terminal transaction statuses in the helper JSDoc, and exports the helper through the public types barrel.

How to test?

Run:

bun test tests/types/transaction-status.test.ts
bun run test
bun run lint

Checklist

• My code follows the code style of this project.
• I have added tests for my changes.
• I have updated the documentation accordingly.
• I have run bun run test and bun run lint locally.

Issue Reference

Closes #131

[gemini-code-assist]

Code Review

This pull request introduces the isTerminalTransactionStatus helper function and a list of terminal transaction statuses, supported by new unit tests. Feedback suggests enhancing type safety by defining a TerminalTransactionStatus union type and implementing the helper as a TypeScript Type Guard. Additionally, it is recommended to refactor the tests to iterate over the TRANSACTION_STATUSES array rather than using hardcoded lists to ensure long-term maintainability and prevent desynchronization.