TGA: Support for TGA specification 2.0

Adds TGA 2.0 compliance:
- Support for Extension Area, Developer Area and Footer (metadata support)
- Support for 15-bit and 16-bit per pixel images (both RGB and Indexed)
- Full support for rotation on reading (we cannot use Qt transformations because only a subset is part of the TGA specification)
- When writing you can choose the supported version (subType)
- Improved writing speed (approximately 10 times) and removed whole image conversions (significant memory savings)

It pass the [TrueVision TGA 2.0 conformance suite](https://github.com/zigimg/test-suite/tree/master/fixtures/tga).

Test changes:
- Read test: added ability to skip a specific test on sequential devices (via JSON behavior file)
- Write test: added the ability to set the subType when writing (via JSON properties file)

Closes #37

autotests/read/tga/extarea.tga.json

@@ -0,0 +1,32 @@
+[
+    {
+        "fileName" : "extarea.png",
+        "skipSequential" : true,
+        "metadata" : [
+            {
+                "key" : "Title",
+                "value" : "Test Card"
+            },
+            {
+                "key" : "Author",
+                "value" : "KDE Project"
+            },
+            {
+                "key" : "ModificationDate",
+                "value" : "2025-08-21T07:32:45"
+            },
+            {
+                "key" : "Comment",
+                "value" : "TV broadcast test image."
+            },
+            {
+                "key" : "Software",
+                "value" : "LIFE Pro 2.18.31 (Linux)"
+            }
+        ],
+        "resolution" : {
+            "dotsPerMeterX" : 3937,
+            "dotsPerMeterY" : 3937
+        }
+    }
+]