Fix compile-time issue involving implicit declaration of mapclut_paletee() (#1648)

* Fix implicit declaration error on some systems.

This commit fixes a compile-time error regarding an implicit declaration
of mapclut_paletee() on some compilers and compiler versions.  Notably,
Arch Linux and Ubuntu 24.10 seem to be affected.

The error resolved is:

```
../src/lib_ccx/ocr.c: In function 'ocr_rect':
../src/lib_ccx/ocr.c:922:9: error: implicit declaration of function 'mapclut_paletee' [-Wimplicit-function-declaration]
  922 |         mapclut_paletee(palette, alpha, (uint32_t *)rect->data1, rect->nb_colors);
      |         ^~~~~~~~~~~~~~~
```

This was resolved by `#include`-ing "ccx_encoders_spupng.h" in the file
src/lib_ccx/ocr.c.  Thanks to GitHub user @steel-bucket for sharing the
fix in this issue's comments.

Fixes: #1646

* Update CHANGES.TXT.

Mention the fix for #1646.

Fixes: #1646

Author: rhymeswithmogul

docs/CHANGES.TXT

@@ -36,6 +36,7 @@
 - Improvement: Use Corrosion to build Rust code
 - Improvement: Ignore MXF Caption Essence Container version byte to enhance SRT subtitle extraction compatibility
 - New: Add tesseract page segmentation modes control with `--psm` flag
+- Fix: Resolve compile-time error about implicit declarations (#1646)
 
 0.94 (2021-12-14)
 -----------------

src/lib_ccx/ocr.c

@@ -7,6 +7,7 @@
 #include "ccx_common_constants.h"
 #include <dirent.h>
 #include "ccx_encoders_helpers.h"
+#include "ccx_encoders_spupng.h"
 #include "ocr.h"
 #undef OCR_DEBUG