feat: add I2_S GGUF conversion for bitnet-b1.58-2B-4T and refactor T-MAC LUT path

- Add quantize_to_i2_s() for direct ternary-to-I2_S packing in conversion script
- Support offline-quantized models (uint8 packed weights + weight_scale)
- Fix weight_quant double-quantization bug for offline-quantized models
- Fix I2_S scale computation to use first nonzero absolute value
- Add I2_S ftype mapping and BitNetForCausalLM registration
- Refactor ggml-bitnet-lut T-MAC wrapper with proper mul_mat implementation
- Update llama.cpp submodule with I2_S ftype and 2B model type support

include/kernel_config.ini

@@ -0,0 +1,21 @@
+[Kernels_0]
+m = 3200
+k = 8640
+bm = 160
+bk = 96
+bmm = 32
+
+[Kernels_1]
+m = 3200
+k = 3200
+bm = 320
+bk = 96
+bmm = 32
+
+[Kernels_2]
+m = 8640
+k = 3200
+bm = 320
+bk = 96
+bmm = 32
+