Refine detection idiom and type traits

[renatoGarcia]

• Add nonesuch sentinel type; use it as default in detected_or instead of void, making "not detected" cases unambiguous
• Rename returned_type -> invoke_result, resolve_view_t -> pipe_result to follow STL naming conventions
• Make get_iterator_t and get_reference_t safe via detected_or instead of hard decltype aliases, preventing hard errors in SFINAE contexts when T is not a range/iterator
• Replace is_input_iterator_expr void_t pattern with is_detected_exact checks enforcing that pre-increment returns T& and post-increment returns T
• Replace bidirectional_iterator_extra_expr with is_detected_exact checks for pre/post decrement return types
• Add is_detected_exact comment and normalize its template formatting
• Strengthen is_sentinel_for to also require I satisfies is_input_iterator