Eliminate benchmark deprecation warnings

Resolve the following warnings issue by the latest version of the
benchmark library:

/Users/runner/work/ceres-solver/ceres-solver/internal/ceres/small_blas_gemv_benchmark.cc:71:54: warning: 'Benchmark' is deprecated: Use ::benchmark::Benchmark instead [-Wdeprecated-declarations]
   71 | static void MatrixSizeArguments(benchmark::internal::Benchmark* benchmark) {
      |

/Users/runner/work/ceres-solver/ceres-solver/internal/ceres/dense_linear_solver_benchmark.cc:67:46: warning: 'Benchmark' is deprecated: Use ::benchmark::Benchmark instead [-Wdeprecated-declarations]
   67 | static void MatrixSizes(benchmark::internal::Benchmark* b) {
      |

/Users/runner/work/ceres-solver/ceres-solver/internal/ceres/invert_psd_matrix_benchmark.cc:80:37: warning: 'Benchmark' is deprecated: Use ::benchmark::Benchmark instead [-Wdeprecated-declarations]
   80 |     ->Apply([](benchmark::internal::Benchmark* benchmark) {
      |

Change-Id: Ice6fe57dc5635698809e368fda23a018f4d7df5a

internal/ceres/dense_linear_solver_benchmark.cc

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2023 Google Inc. All rights reserved.
+// Copyright 2026 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -64,7 +64,7 @@ static void BM_DenseSolver(benchmark::State& state) {
 }
 
 // Some reasonable matrix sizes. I picked them out of thin air.
-static void MatrixSizes(benchmark::internal::Benchmark* b) {
+const auto MatrixSizes = [](auto* b) {
   // {num_rows, num_cols}
   b->Args({1, 1});
   b->Args({2, 1});
@@ -82,7 +82,7 @@ static void MatrixSizes(benchmark::internal::Benchmark* b) {
   b->Args({400, 20});
   b->Args({600, 22});
   b->Args({800, 25});
-}
+};
 
 BENCHMARK_TEMPLATE2(BM_DenseSolver, ceres::EIGEN, ceres::DENSE_QR)
     ->Apply(MatrixSizes);

internal/ceres/invert_psd_matrix_benchmark.cc

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2023 Google Inc. All rights reserved.
+// Copyright 2026 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -76,12 +76,11 @@ static void BenchmarkDynamicallyInvertPSDMatrix(benchmark::State& state) {
   }
 }
 
-BENCHMARK(BenchmarkDynamicallyInvertPSDMatrix)
-    ->Apply([](benchmark::internal::Benchmark* benchmark) {
-      for (int i = 1; i < 13; ++i) {
-        benchmark->Args({i});
-      }
-    });
+BENCHMARK(BenchmarkDynamicallyInvertPSDMatrix)->Apply([](auto* benchmark) {
+  for (int i = 1; i < 13; ++i) {
+    benchmark->Args({i});
+  }
+});
 
 }  // namespace ceres::internal
 

internal/ceres/small_blas_gemv_benchmark.cc

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2023 Google Inc. All rights reserved.
+// Copyright 2026 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -68,7 +68,7 @@ class MatrixVectorMultiplyData {
 
 // Helper function to generate the various matrix sizes for which we
 // run the benchmark.
-static void MatrixSizeArguments(benchmark::internal::Benchmark* benchmark) {
+const auto MatrixSizeArguments = [](auto* benchmark) {
   std::vector<int> rows = {1, 2, 3, 4, 6, 8};
   std::vector<int> cols = {1, 2, 3, 4, 8, 12, 15};
   for (int r : rows) {
@@ -76,9 +76,10 @@ static void MatrixSizeArguments(benchmark::internal::Benchmark* benchmark) {
       benchmark->Args({r, c});
     }
   }
-}
+};
 
-static void BM_MatrixVectorMultiply(benchmark::State& state) {
+static void
+BM_MatrixVectorMultiply(benchmark::State & state) {
   const int rows = state.range(0);
   const int cols = state.range(1);
   MatrixVectorMultiplyData data(rows, cols);