Allow lowercase letters for array tool pin numbering

The ARRAY_AXIS class now accepts lowercase letters (a-z) as input for
alphabetic numbering schemes and preserves that case in the output.
This allows users to create pin numbers like a1, b1, c1 which are
commonly used in DIN 41612 and other backplane connectors.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/22787

qa/tests/common/test_array_axis.cpp

@@ -105,6 +105,32 @@ BOOST_AUTO_TEST_CASE( ValidOffsets )
             false,
             0,
         },
+        // Lowercase alphabetical input should be accepted and map to same offset as uppercase
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_FULL,
+            "a",
+            true,
+            0,
+        },
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_FULL,
+            "xy",
+            true,
+            648,
+        },
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_NO_IOSQXZ,
+            "a",
+            true,
+            0,
+        },
+        // Hex lowercase should NOT be accepted (hex only allows uppercase A-F)
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_HEX,
+            "a0",
+            false,
+            0,
+        },
     };
     // clang-format on
 
@@ -187,6 +213,39 @@ static const std::vector<ARRAY_AXIS_NAMING_CASE> axis_name_cases = {
         6,
         { "11", "13", "15", "17", "19", "21" },
     },
+    {
+        // Test lowercase alphabetical input produces lowercase output
+        "Alpha lowercase",
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_FULL,
+            "a",
+            1,
+        },
+        3,
+        { "a", "b", "c" },
+    },
+    {
+        // Test lowercase alphabetical with 2nd col
+        "Alpha lowercase 2nd col",
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_FULL,
+            "y",
+            1,
+        },
+        4,
+        { "y", "z", "aa", "ab" },
+    },
+    {
+        // Test lowercase no-IOSQXZ alphabet
+        "Alpha no IOSQXZ lowercase",
+        {
+            ARRAY_AXIS::NUMBERING_TYPE::NUMBERING_ALPHA_NO_IOSQXZ,
+            "a",
+            1,
+        },
+        5,
+        { "a", "b", "c", "d", "e" },
+    },
 };
 // clang-format on