When calling an intersection type where all callable elements reject
the specific call arguments, we now show an error for each failing
element (similar to how unions work) instead of a single generic
"not callable" error.
This is achieved by:
- Not filtering out failed elements when ALL elements fail
- Returning BindingError instead of NotCallable to trigger individual diagnostics
- Adding IntersectionDiagnostic struct and CompoundDiagnostic trait
- Modifying report_diagnostics to iterate over intersection elements
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