Configure clang-format include ordering with IncludeCategories

Change IncludeBlocks from Preserve to Regroup and define priority
categories to enforce consistent include ordering: global.hpp first,
then standard library headers, then third-party headers, then project
headers.

🤖 Commit message by [Claude Code](https://claude.com/claude-code)

Author: laurynas-biveinis

.clang-format

@@ -1,7 +1,16 @@
 ---
 Standard: c++20
 BasedOnStyle: Google
-IncludeBlocks: Preserve
+IncludeBlocks: Regroup
+IncludeCategories:
+  - Regex: '^"global\.hpp"$'
+    Priority: -1
+  - Regex: '^<[a-z_]+>$'
+    Priority: 2
+  - Regex: '^<.*>$'
+    Priority: 3
+  - Regex: '^".*"$'
+    Priority: 4
 AttributeMacros:
   - UNODB_DETAIL_UNUSED
   - UNODB_DETAIL_USED_IN_DEBUG

art_internal.cpp

@@ -5,14 +5,13 @@
 
 // IWYU pragma: no_include <__ostream/basic_ostream.h>
 
-#include "art_internal.hpp"  // IWYU pragma: keep
-
-#include "art_common.hpp"
-
 #include <cstddef>
 #include <iomanip>
 #include <iostream>  // IWYU pragma: keep
 
+#include "art_common.hpp"
+#include "art_internal.hpp"  // IWYU pragma: keep
+
 namespace unodb::detail {
 
 [[gnu::cold]] UNODB_DETAIL_NOINLINE void dump_byte(std::ostream &os,

benchmark/micro_benchmark.cpp

@@ -15,10 +15,9 @@
 
 #include "art_common.hpp"
 #include "art_internal.hpp"  // IWYU pragma: keep
-#include "node_type.hpp"
-
 #include "micro_benchmark_node_utils.hpp"
 #include "micro_benchmark_utils.hpp"
+#include "node_type.hpp"
 
 namespace {
 

qsbr.cpp

@@ -14,8 +14,6 @@
 // IWYU pragma: no_include <__new/exceptions.h>
 // IWYU pragma: no_include <__hash_table>
 
-#include "qsbr.hpp"
-
 #include <atomic>
 #include <cstdint>
 #include <exception>
@@ -24,6 +22,8 @@
 #include <new>  // IWYU pragma: keep
 #include <utility>
 
+#include "qsbr.hpp"
+
 #ifdef UNODB_DETAIL_WITH_STATS
 #include <mutex>
 #endif  // UNODB_DETAIL_WITH_STATS

test/db_test_utils.hpp

@@ -28,12 +28,11 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-#include "gtest_utils.hpp"
-
 #include "art.hpp"
 #include "art_common.hpp"
 #include "art_internal.hpp"
 #include "assert.hpp"
+#include "gtest_utils.hpp"
 #include "mutex_art.hpp"
 #include "node_type.hpp"
 #include "olc_art.hpp"

test/qsbr_gtest_utils.cpp

@@ -6,7 +6,6 @@
 #include "qsbr_gtest_utils.hpp"  // IWYU pragma: keep
 
 #include "qsbr.hpp"
-
 #include "qsbr_test_utils.hpp"
 
 namespace unodb::test {