Add #pragma once to all header files

This change implements the LinksPlatform decision to use #pragma once
instead of traditional header guards in all C++ headers. The following
files were updated:

- cpp/Platform.Ranges/Range.h: Added #pragma once
- cpp/Platform.Ranges/Range[T].h: Added #pragma once
- cpp/Platform.Ranges/EnsureExtensions.h: Added #pragma once
- cpp/Platform.Ranges/RangeExtensions.h: Added #pragma once
- cpp/Platform.Ranges.Tests/pch.h: Replaced traditional guards with #pragma once

This provides cleaner, more maintainable header protection across the codebase
while ensuring compatibility with modern C++ compilers.

Fixes #43

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: konard

cpp/Platform.Ranges.Tests/pch.h

@@ -4,9 +4,6 @@
 // However, files listed here are ALL re-compiled if any one of them is updated between builds.
 // Do not add files here that you will be updating frequently as this negates the performance advantage.
 
-#ifndef PCH_H
-#define PCH_H
+#pragma once
 
 // add headers that you want to pre-compile here
-
-#endif //PCH_H

cpp/Platform.Ranges/EnsureExtensions.h

@@ -1,4 +1,6 @@
-namespace Platform::Ranges::Ensure::Always
+#pragma once
+
+namespace Platform::Ranges::Ensure::Always
 {
     const std::string DefaultMaximumShouldBeGreaterOrEqualToMinimumMessage = "Maximum should be greater or equal to minimum.";
 

cpp/Platform.Ranges/Range.h

@@ -1,4 +1,6 @@
-namespace Platform::Ranges
+#pragma once
+
+namespace Platform::Ranges
 {
     #define LIMIT_AS_RANGE(type) std::numeric_limits<type>::lowest(), std::numeric_limits<type>::max()
 

cpp/Platform.Ranges/RangeExtensions.h

@@ -1,4 +1,6 @@
-namespace Platform::Ranges
+#pragma once
+
+namespace Platform::Ranges
 {
     template<typename T> requires requires(T a, T b) { a - b; }
     auto Difference(Range<T> range)

cpp/Platform.Ranges/Range[T].h

@@ -1,4 +1,6 @@
-namespace Platform::Ranges
+#pragma once
+
+namespace Platform::Ranges
 {
     namespace Internal
     {