WASHINGTON — Some of Illinois Rep. Aaron Schock’s current and previous employees will appear before a federal grand jury next month to answer questions about their old boss. When they do, they’ll likely face a prosecutor with a tough, meticulous reputation.Timothy Allen Bass, a 20-year veteran prosecutor who’s involved in the investigation, is known for combing through every detail of his cases. He’s prosecuted drug and gun crimes, money laundering, tax evasion, child pornography …