Let Profiling::ProfilingSection(std::string) constructor be explicit and nodiscard

[dalg24]

Rational: mostly consistency

This aligns with what we did for ScopedRegion

kokkos/core/src/Kokkos_Profiling_ScopedRegion.hpp

Lines 31 to 38 in 2ac06ce

	class [[nodiscard]] ScopedRegion {
	public:
	ScopedRegion(ScopedRegion const &) = delete;
	ScopedRegion &operator=(ScopedRegion const &) = delete;
	#if defined(__has_cpp_attribute) && __has_cpp_attribute(nodiscard) >= 201907
	[[nodiscard]]
	#endif

The nodiscard attribute will warn on a common beginner error to "forget" to give the scope guard variable a name (although admittedly creating a section without calling start/stop is unlikely so that error would not occur in practice).

If we do any change at all, we might as well mark the constructor as explicit.

[crtrott]

Retest this please.

[dalg24]

Ignoring Jenkins CI