ggml: use dynamic allocation for split graph inputs (#22789)

ggml: use dynamic allocation for split graph inputs (#22789)

* ggml: use dynamic allocation for split graph inputs

Replace fixed-size GGML_SCHED_MAX_SPLIT_INPUTS arrays with dynamically
allocated buffers in the backend scheduler. This fixes crashes when
loading wide MoE models (Gemma 4, Qwen MoE, Mixtral, DeepSeek) on
multi-backend setups where graph splits exceed 30 input tensors.

- split->inputs: dynamic array with grow-on-demand
- sched->graph_inputs: dynamic array with grow-on-demand
- graph_size calculation now uses actual input count instead of fixed constant

* cont : clean-up

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Co-authored-by: Georgi Gerganov <redacted>