Refactor benchmark and support LongMemEval

[starboyate]

Summary

• consolidate benchmark logic into memind-evaluation and remove the legacy memind-benchmark module
• add dataset profile/config support for LoCoMo and LongMemEval, including query building, evaluator wiring, and batch/checkpoint improvements
• harden vector and JDBC persistence paths and add regression coverage for LongMemEval conversion and insight flush behavior

Test Plan

• mvn test