[DeePrincipal-dev-lang]

Title: Fix market purchase state ordering around token transfers

Description

Summary

Update the market purchase flow to follow checks-effects-interactions and ensure a failed token transfer does not leave a purchase recorded.

Changes

• Validate the buyer and product, acquire the reentrancy lock, then update the product, listing, and purchase record before calling the token contract.
• Keep the lock held during the external token call.
• Add successful and failing token stubs for purchase tests.
• Add a regression test verifying a failed transfer leaves the product unsold, the listing available, no purchase record created, and the lock released.

Validation

• git diff --check passed; editor diagnostics reported no errors.
• cargo test -p market and the Rust pre-commit checks could not run because cargo is unavailable in the environment.

closes #1315