add reference benchmark dimensions for Quadtrix (#39)

## Summary
Introduces configuration for real C++ and Python Quadtrix benchmark
runs, including warmup, token generation, and training step dimensions.

Author: Eamon2009

benchmark/benchmark_config.json

@@ -0,0 +1,59 @@
+{
+  "schema_version": 1,
+  "purpose": "Reference benchmark dimensions for the real C++ and Python Quadtrix benchmark suites.",
+  "common": {
+    "runs": 10,
+    "warmup": 3,
+    "quick_runs": 2,
+    "quick_warmup": 1,
+    "generate_tokens": 32,
+    "quick_generate_tokens": 4,
+    "train_steps": 5,
+    "quick_train_steps": 1,
+    "max_data_chars": 1000000,
+    "quick_max_data_chars": 50000
+  },
+  "suites": {
+    "data": [
+      "tokenizer_or_char_encode",
+      "batch_sample_to_device"
+    ],
+    "primitive": [
+      "matmul_3d",
+      "attention_scores_or_softmax3d",
+      "layer_norm"
+    ],
+    "forward": [
+      "batch1_seq8",
+      "batch1_full_context",
+      "configured_batch_full_context"
+    ],
+    "training": [
+      "adamw_step_forward_backward_update"
+    ],
+    "generation": [
+      "empty_prompt",
+      "short_prompt",
+      "long_prompt"
+    ]
+  },
+  "metrics": [
+    "avg_ms",
+    "median_ms",
+    "min_ms",
+    "max_ms",
+    "p90_ms",
+    "p95_ms",
+    "std_ms",
+    "tokens_per_sec",
+    "loss",
+    "parameter_mb_fp32",
+    "memory_mb"
+  ],
+  "outputs": {
+    "cpp_json": "benchmark/results/cpp_benchmark.json",
+    "cpp_csv": "benchmark/results/cpp_benchmark.csv",
+    "python_json": "benchmark/results/python_benchmark.json",
+    "python_csv": "benchmark/results/python_benchmark.csv"
+  }
+}