Implement transaction simulation in VaultModule.withdraw

[Code-Paragon]

Problem

Similar to the deposit method, the withdraw method constructs and submits a transaction immediately without utilizing Soroban's simulation endpoint first to check for execution failures.

Expected behavior

The withdraw method simulates the transaction. If it fails (e.g., due to an insufficient ysToken balance), it throws a descriptive error protecting the user from paying a failed gas fee.

Files to update

• src/modules/vault.ts

Project relevance

Ensures capital efficiency for Keepers and LPs by providing immediate, off-chain feedback before on-chain submission occurs.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• An explicit check for simulation failure is present before buildAndSubmit is invoked
• No TypeScript, lint, test, or build errors