chore: import upstream snapshot with attribution

tensorflow/lite/delegates/ynnpack/README.md

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+# YNNPACK Delegate for LiteRT
+
+> [!WARNING]
+> The YNNPACK delegate is **experimental** and under active development. Expect
+> bugs and performance issues when using it.
+
+The YNNPACK delegate allows LiteRT (formerly TensorFlow Lite) to offload
+supported operators to YNNPACK.
+
+YNNPACK aims to provide great flexibility with good performance.
+
+## Delegate Provider Options
+
+When using LiteRT tooling (e.g., benchmarks, evaluation tools) that link the
+`ynnpack_delegate_provider`, the following command-line flags are exposed to
+configure the YNNPACK delegate:
+
+### Core Options
+
+*   **`--use_ynnpack=true|false`** (default: `false`):
+    Explicitly apply the YNNPACK delegate to the model.
+
+*   **`--num_threads=N`** (default: `0` or `1` depending on tool):
+    The number of threads to use for execution. Note that YNNPACK will only use
+    a thread pool for `num_threads > 1`. A value of `0` or `1` disables the
+    thread pool (single-threaded execution).
+
+### YNNPACK Specific Options
+
+*   **`--ynnpack_static_shape=true|false`** (default: `false`):
+    Make input shapes static instead of dynamic. Enabling this may improve
+    execution (`Invoke`) performance by allowing YNNPACK to optimize for fixed
+    shapes, but it makes model reshaping (`ResizeInputTensor`) much more
+    expensive.
+
+*   **`--ynnpack_fast_math=true|false`** (default: `false`):
+    Enable `YNN_FLAG_FAST_MATH`. This allows YNNPACK to use faster but
+    potentially less precise mathematical approximations.
+
+*   **`--ynnpack_consistent_arithmetic=true|false`** (default: `false`):
+    Enable `YNN_FLAG_CONSISTENT_ARITHMETIC`. YNNPACK will attempt to provide
+    numerically consistent results for all hardware the **same build** of
+    YNNPACK runs on. It does not guarantee consistency across different builds
+    (which means it does not guarantee consistency across different platforms,
+    which are necessarily different builds).
+
+*   **`--ynnpack_no_excess_precision=true|false`** (default: `false`):
+    Enable `YNN_FLAG_NO_EXCESS_PRECISION`. YNNPACK will not promote tensors to
+    higher precision as a performance optimization.