Match strong typedef copy constructor exception guarantees

[mikamikasuki]

The value constructor taking const T& is currently reported as potentially throwing even when copying T cannot throw. Give it noexcept(std::is_nothrow_copy_constructible<T>::value), matching the existing conditional guarantee on the move constructor.

The regression covers six copy/move trait combinations and checks that throwing copies and moves still propagate their exceptions.

Validation with Apple Clang 16 on macOS:

• Full Debug suite: 49 test cases, 2834 assertions. Full Release suite: 49 test cases, 2797 assertions.
• Strict C++11, 14, 17, 20, and 23 consumers pass -Wall -Wextra -Werror -pedantic-errors.
• Focused copy/move exception checks pass ASan/UBSan.

Fixes #167.

Prepared with AI assistance.