how to write configs of custom tests for a new insn

I'm not very familiar with Go. Right now, I have a custom instruction and I want to use this project to automatically generate test cases for it.
I know I need to create a config file like `configs/xxx.toml` for my new instruction, but I'm not exactly sure how to write it.

I looked at an example:

```toml
name = "vwadd.vv"
format = "vd,vs2,vs1,vm"

[tests]
base = [
[0x0, 0x0],
[0x1, 0x2],
[0x3, 0xf]
]
sew8 = [
[0xf8, 0x00],
[0xf8, 0x08],
[0x7f, 0x00],
[0x7f, 0x07],
[0x7f, 0x01],
[0xff, 0x00],
[0xff, 0xff]
]
```
The part I don't really get is what the numbers under the [tests] section mean.
How are they used when generating the actual test cases?
Could you help me understand that?

Start with the example in configs/xxx.toml, especially the [tests] section, and trace how its values are used when generating actual test cases. Document what the numbers represent, how the base and sew8 entries differ, and how someone should configure a new instruction.

Written by the indexing model from the issue text.