compiler: resolve panic in substituteTypeArgs Function for `*ast.IndexListExpr`

[iamrajiv]

Fixes: #141

This PR addresses a panic occurring in the substituteTypeArgs function within the types.go file. The panic is caused by the lack of handling for the *ast.IndexListExpr type, resulting in unexpected behavior during type substitution.

[iamrajiv]

I don't think @achille-roussel that we need a test for this because there are other cases in substituteTypeArgs for which tests were not added, so I'll just follow the same approach of not adding tests. But if you want, I can write a test for all the cases defined in the substituteTypeArgs function.

[achille-roussel]

Also to follow up on this:

there are other cases in substituteTypeArgs for which tests were not added

The git history may look like that was the case, but it's missing context about in-person development that happened at the time the project was being bootstrapped before it was made public. In general, we have strong test coverage for the features we support, and we maintain a rigorous testing culture to ensure we can continue to provide a high quality solution over time 👍

[chriso]

Fixed by https://github.com/dispatchrun/coroutine/pull/148