Add precision-loss and fractional slippage test scenarios

[Code-Paragon]

Problem

The CONTRIBUTING.md requires precision-loss checks, but the current test.rs only uses clean, round numbers (1000, 100), completely ignoring integer truncation risks in Soroban's i128 math.

Expected behavior

A new test scenario deposits highly fragmented, prime-number liquidity values, processes a fractional yield harvest, and withdraws to prove that truncation does not result in trapped dust.

Files to update

• src/test.rs

Project relevance

Guarantees the mathematical integrity of the fractional-reserve exchange rate model, proving that integer division rounding heavily favors the protocol over attackers.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• The test asserts that the Vault's remaining underlying_balance is >= 0 after all shares are burned
• No TypeScript, lint, test, or build errors