signed/unsigned mismatch in tested kernels.

There are 557 instances of code like this:

```cpp
int tid = get_global_id(0);
```
But get_global_id returns size_t, so it's unsigned.

Some compilers (like Clspv) will warn on this.

The code should be updated. I don't have an opinion about whether tid should be changed to unsigned (or size_t), or whether to cast the value.

Search the tested kernels for instances such as `int tid = get_global_id(0)` and review how each value is used before choosing a consistent type or cast. Run the relevant OpenCL conformance tests and compiler checks to confirm the signed/unsigned warnings are addressed across the affected kernels.

Written by the indexing model from the issue text.