Update layer package convention naming

Accept camelCase regarding Kotlin guidelines.
https://kotlinlang.org/docs/coding-conventions.html#naming-rules

Author: BapNesS

lib/src/main/kotlin/com/lemonappdev/konsist/api/architecture/Layer.kt

@@ -100,7 +100,7 @@ data class Layer(
                     "Invalid package definition for layer '$name'. " +
                         "Invalid package segment '$segment' at position ${index + 1}. " +
                         "Package segments must start with a lowercase letter and contain only " +
-                        "lowercase letters, numbers, or underscores. Current definition: $rootPackage",
+                        "letters, numbers, or underscores. Current definition: $rootPackage",
                 )
             }
         }
@@ -119,6 +119,6 @@ data class Layer(
             "the definition must end with '..'. Current definition: $rootPackage"
 
     private companion object {
-        private val REGEX_VALID_PACKAGE_SEGMENT = Regex("^[a-z][a-z0-9_]*$")
+        private val REGEX_VALID_PACKAGE_SEGMENT = Regex("^[a-z][a-zA-Z0-9_]*$")
     }
 }

lib/src/test/kotlin/com/lemonappdev/konsist/api/architecture/LayerTest.kt

@@ -56,7 +56,7 @@ class LayerTest {
     }
 
     @Test
-    fun `create Layer with uppercase package segment should throw exception`() {
+    fun `create Layer with Pascal case package segment should throw exception`() {
         // when
         val func = { Layer(name = "name", rootPackage = "Com.example..") }
 
@@ -111,6 +111,7 @@ class LayerTest {
                 "com.example.test..",
                 "com.example1.test2..",
                 "com.example_test..",
+                "com.exampleTest..",
             )
 
         // then