Could we number only the problem line?

When reporting errors with project files (and cabal files):

```
1 | packages: .
2 |
3 | -- This is an error; a trailing `:` is syntax for a field, not a stanza!
4 | source-repository-package:
| ^
```

Do we need all of lines 1..4? Could we number only the problem line and include the lines above and below, unnumbered. This is what GHC does, isn't it?

_Originally posted by @philderbeast in https://github.com/haskell/cabal/pull/8889#discussion_r2213579263_