Add clang-format to format C# files

.clang-format

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+BasedOnStyle: Google
+---
+Language: CSharp
+ColumnLimit: 100

.pre-commit-config.yaml

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+repos:
+  - repo: https://github.com/pre-commit/mirrors-clang-format
+    rev: v18.1.8
+    hooks:
+      - id: clang-format