llama: add Maple 20B-A1B ternary MoE architecture (CPU) (#27000)

* gguf-py: add Maple tensor constants

Add MODEL_ARCH.MAPLE, its "maple" name, and the tensor list for the
Maple 20B-A1B ternary MoE architecture: token embeddings, output,
attention with Q/K RMS norms, and per-expert FFN tensors.

* convert: add Maple HF->GGUF converter

Register MapleForCausalLM in the HF architecture map and add the
converter for the Maple 20B-A1B ternary MoE model: 24 layers, 256
experts with 8 active, sliding-window attention (SWA-512) interleaved
with global attention at a 3:1 ratio, partial rotary factor 0.5, and
per-expert weight stacking into merged 3D tensors.

* llama: add Maple architecture (20B-A1B ternary MoE)

Add the Maple 20B-A1B ternary MoE architecture: 24 layers, 256
experts with 8 active, sliding-window attention (SWA-512) interleaved
with global attention at a 3:1 ratio, and ternary TQ1_0/TQ2_0
quantization support.

- register LLM_ARCH_MAPLE between MAMBA2 and JAMBA
- implement llama_model_maple: Q/K RMS norms after projection (GEMMA4
  style), rope applied only on SWA layers (nope_on_global_attention),
  ISWA KV cache, and MoE FFN with swiglu gate clamp at +7 (DEEPSEEK4
  style)
- mark MAPLE as unsupported by the model saver (roundtrip skipped)

* tests: mark Maple as MoE-mandatory

Maple is always-MoE: the model throws when n_expert == 0, so the
test harness must only run the MoE config for LLM_ARCH_MAPLE.

* maple: apply review feedback (n_ff_exp_arr, get_arr, rope params)

- load_arch_hparams: use n_ff_exp_arr + n_ff_exp() accessor (upstream
  changed these from a scalar member during the rebase)
- sliding_window_pattern: get_arr, the pattern is mandatory for this arch
- partial_rotary_factor: read only from rope_parameters (base.py mirrors
  the top-level key automatically)
- document why TOKEN_EMBD/OUTPUT are forced to F16 (they are the two
  dense tensors in Maple, and the reference GGUFs ship them as F16)
- add @ModelBase.example("deepgrove/maple-preview")

* tests: add Maple to the SWA pattern array list

get_arr for maple.attention.sliding_window_pattern requires an array, but
the harness only emitted a per-layer array for the arches in its list, so
test-llama-archs -a maple failed to load the model.

Assisted-by: DeepSeek Harness

* maple: move swiglu_clamp_exp to the converter

The loader prefilled 7.0 and read the key optionally. The converter now
writes it and the loader reads it as required, because llama-graph.cpp
skips the clamp when the limit is 0 and an optional read would silently
run unclamped. The test harness provides the key for the same reason.

Also drops tensor_force_quant: base.py already forces FFN_GATE_INP to F32
and TOKEN_EMBD/OUTPUT to F16 for ternary file types.

Assisted-by: DeepSeek Harness

* convert: fix the LazyBase func signature in the Maple converter

ty flagged the stack() closure: it takes no argument, while LazyBase is
annotated with func: Callable[[Any], Any]. Pass the tensor list through
args instead of closing over it, the same way kimi_k3 does, so the
callable shape matches.

Assisted-by: DeepSeek Harness

tests/test-llama-archs.cpp

@@ -239,7 +239,8 @@ static gguf_context_ptr get_gguf_ctx(const llm_arch arch, const bool moe) {
         // SWA pattern: every 5th layer is full attention (matches E2B layer_types)
         ms.add_kv(LLM_KV_ATTENTION_SLIDING_WINDOW_PATTERN, uint32_t(5));
     } else if (arch == LLM_ARCH_COHERE2MOE || arch == LLM_ARCH_MIMO2 || arch == LLM_ARCH_STEP35 || arch == LLM_ARCH_SPARK2_5 ||
-            arch == LLM_ARCH_MUSE_GLIMMER || arch == LLM_ARCH_GRANITE_SWA || arch == LLM_ARCH_DOTS3NOTE) {
+            arch == LLM_ARCH_MUSE_GLIMMER || arch == LLM_ARCH_GRANITE_SWA || arch == LLM_ARCH_DOTS3NOTE ||
+            arch == LLM_ARCH_MAPLE) {
         std::vector<uint32_t> pattern;
         pattern.reserve(n_layer);
         for (uint32_t il = 0; il < n_layer; il++) {
@@ -323,6 +324,11 @@ static gguf_context_ptr get_gguf_ctx(const llm_arch arch, const bool moe) {
         ms.add_kv(LLM_KV_EXPERT_WEIGHTS_SCALE,                  1.0f);
         ms.add_kv(LLM_KV_EXPERT_WEIGHTS_NORM,                   true);
     }
+
+    if (arch == LLM_ARCH_MAPLE) {
+        ms.add_kv(LLM_KV_SWIGLU_CLAMP_EXP, 7.0f);
+    }
+
     ms.add_kv(LLM_KV_TOKENIZER_MODEL,         "no_vocab");
     // ms.add_kv(LLM_KV_DENSE_2_FEAT_OUT,     n_embd);
     // ms.add_kv(LLM_KV_DENSE_3_FEAT_IN,      n_embd);
@@ -505,6 +511,7 @@ static bool moe_mandatory(const llm_arch arch) {
         case LLM_ARCH_MISTRAL4:
         case LLM_ARCH_MELLUM:
         case LLM_ARCH_LAGUNA:
+        case LLM_ARCH_MAPLE:
             return true;
         default:
             return false;