Add BigInt parameter tests to math.test.ts

[Code-Paragon]

Problem

The fromStroops function accepts a bigint parameter, but math.test.ts only currently asserts against string inputs.

Expected behavior

The test suite includes assertions verifying that native JavaScript BigInt objects passed into fromStroops correctly convert into decimal strings without precision loss.

Files to update

• tests/math.test.ts

Project relevance

Soroban i128 values return as BigInts via the XDR parser; testing this integration directly secures the math pipeline against rounding bugs.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• expect(fromStroops(105000000n)).toBe("10.5000000") or equivalent BigInt assertion is added
• No TypeScript, lint, test, or build errors