llama : rename llama-sampling to llama-sampler (#19363)

This commit addresses the TODO in llama-sampling.h to rename that header
and the implementation to llama-sampler.

src/llama-sampler.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "llama.h"
+
+#include <vector>
+
+struct llama_vocab;
+struct llama_grammar;
+
+// sampler chain
+
+struct llama_sampler_chain {
+    llama_sampler_chain_params params;
+
+    // has .backend_init() been called?
+    bool is_init = false;
+
+    struct info {
+        bool is_backend;
+
+        llama_sampler * ptr;
+    };
+
+    std::vector<info> samplers;
+
+    // pre-allocated buffer for llama_sampler_sample to avoid repeated allocations
+    std::vector<llama_token_data> cur;
+
+    // timing
+
+    mutable int64_t t_sample_us;
+
+    mutable int32_t n_sample;
+};
+
+struct llama_sampler * llama_sampler_init_dry_testing(
+        int32_t context_size,
+        float   dry_multiplier,
+        float   dry_base,
+        int32_t dry_allowed_length,
+        int32_t dry_penalty_last_n,
+        const std::vector<std::vector<llama_token>> & seq_breakers);