Add unit test suite for xdr-parser.ts

[Code-Paragon]

Problem

The xdr-parser.ts file handles critical logic converting raw Soroban results into readable data, but currently lacks any unit tests to ensure it doesn't fail on complex structures.

Expected behavior

A new test suite provides base64 XDR strings of different types (i128, boolean, simple strings) and asserts that parseSorobanResult outputs the expected native TypeScript values.

Files to update

• tests/xdr-parser.test.ts (create)

Project relevance

Parsing blockchain data correctly is the core function of the SDK middleware. Testing this ensures the frontend never displays corrupted data.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• At least 3 distinct XDR base64 mock strings are tested (including an i128 representing a large BigInt)
• No TypeScript, lint, test, or build errors