"<>" in expression language occasionally not allowed?
I don't know how things implemented in fastparse, but wouldn't this code never match `<>` ?
https://github.com/kaitai-io/kaitai_struct_compiler/blob/0f32f3734dad0039dffb2275d38612eb779689ec/shared/src/main/scala/io/kaitai/struct/exprlang/Expressions.scala#L60-L69

In simplified form:
```js
comp_op
  = "<="
  / ">="
  / "=="
  / ">"
  / "<" // if this matched...
  / "<>"// ...that can't be matched
  / "!="
  ;
```

In PEG choice is ordered, so when `<` matched, `<>` won't be even tried