GitLab

* Enable and apply clang-tidy readability and misc fixes.

* Revert deprecated tester

* add space to tests/test_constants_and_functions.cpp

* Add more modernize clang-tidy checks

* Enable a few more

* Apply performance fixes from clang-tidy

* 2nd Round of Perf Optimizations

* 3rd round of fixes & handle false-positive

* Apply missing fix and clang-format

* Apply reviewer comment

```
/pybind11/include/pybind11/iostream.h:71:9: warning: Call to virtual method 'pythonbuf::sync' during destruction bypasses virtual dispatch [clang-analyzer-optin.cplusplus.VirtualCall]
        sync();
        ^
/pybind11/tests/test_iostream.cpp:72:5: note: Calling '~scoped_ostream_redirect'
    });
```