ut: alloc-dealloc-mismatch (operator new [] vs free) in api_server_test

Ref #358
```
==7595==ERROR: AddressSanitizer: alloc-dealloc-mismatch (operator new [] vs free) on 0x60600024df40
```
https://github.com/4paradigm/OpenMLDB/blob/326295840f6c2932c2d47937f8cf0ddf6c238664/hybridse/include/base/fe_slice.h#L104
is new [], we should use delete [], not free.

The issue points to a specific line in hybridse/include/base/fe_slice.h where memory allocated with new[] is incorrectly freed with free. Start by examining that file around line 104 to understand the context. Look for the corresponding deallocation call and replace free with delete[]. Run the api_server_test with address sanitizer to verify the fix resolves the alloc-dealloc-mismatch error.

Written by the indexing model from the issue text.