Refactor knowhere UT

[cydrain]

Target:

1. code coverage > 80%
2. runtime for each case < 5s

https://zilliverse.feishu.cn/wiki/S8JtwBcIyiPWYkkdhqdcJalmnM6 Task items:

• [x] update test_config
• [x] update test_knowhere_init
• [x] update test_index_check
• [x] update test_utils for thread_pool
• [ ] update test_feder for diskann
• [x] add ut for index.h / index_node.h / index_node_xxx.h
• [x] add ut for src/common
• [x] re-write test_simd
• [ ] add test for cluster ( @chasingegg )
• [ ] add test for bruteforce sparse ( @zhengbuqian )
• [ ] add test for index range search ( @zhengbuqian )
• [ ] add test for index iterator ( @zhengbuqian )
• [ ] use trompeloeil to mock index ( @cydrain )