Add a .clang-format file

This uses a line length of 80, because analysis of existing files shows
that the greatest number of lines in the files are 80 chars or less.

Author: mhucka

.clang-format

@@ -0,0 +1,35 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+# Basic clang-format config for this project.
+# See https://clang.llvm.org/docs/ClangFormatStyleOptions.html for more info.
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---
+Language: Cpp
+BasedOnStyle: Google
+ColumnLimit: 80
+AlignAfterOpenBracket: AlwaysBreak
+IncludeCategories:
+  - Regex:           '^<.*>$'
+    Priority:        1
+  - Regex:           '^"gtest/.*"$'
+    Priority:        2
+  - Regex:           '^".*"$'
+    Priority:        3
+IncludeIsMainRegex: '([.](test|benchmark))?$'
+---
+Language: Proto
+BasedOnStyle: Google
+...