Fix: Conditionally export inplaceConvertFrame* functions for testing only

These internal conversion functions are only needed for unit testing and
should not be part of the public API in production builds.

- Added CCAP_TEST_EXPORT macro that expands to CCAP_EXPORT only when CCAP_BUILD_TESTS is ON
- In production builds (CCAP_BUILD_TESTS=OFF), these functions remain internal
- Fixes LNK2019 unresolved external symbol error in shared library test builds
- Ensures cleaner API surface in production releases

Author: wysaid

src/ccap_convert_frame.h

@@ -30,11 +30,18 @@
 /// - Assertion failure in debug builds
 /// - Undefined behavior
 
+// Export internal functions only when building tests
+#ifdef CCAP_BUILD_TESTS
+    #define CCAP_TEST_EXPORT CCAP_EXPORT
+#else
+    #define CCAP_TEST_EXPORT
+#endif
+
 namespace ccap {
 
-bool inplaceConvertFrame(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
-bool inplaceConvertFrameRGB(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
-bool inplaceConvertFrameYUV2RGBColor(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
+CCAP_TEST_EXPORT bool inplaceConvertFrame(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
+CCAP_TEST_EXPORT bool inplaceConvertFrameRGB(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
+CCAP_TEST_EXPORT bool inplaceConvertFrameYUV2RGBColor(VideoFrame* frame, PixelFormat toFormat, bool verticalFlip);
 
 } // namespace ccap