API + Model: Add speculative ngram decoding

Speculative ngram decoding is like speculative decoding without the
draft model. It's not as useful because it only decodes on predictable
sequences, but it depends on the usecase.

Signed-off-by: kingbri <bdashore3@proton.me>

common/sampling.py

@@ -123,6 +123,10 @@ class BaseSamplerRequest(BaseModel):
         default_factory=lambda: get_default_sampler_value("grammar_string"),
     )
 
+    speculative_ngram: Optional[bool] = Field(
+        default_factory=lambda: get_default_sampler_value("speculative_ngram"),
+    )
+
     # Aliased variables
     typical: Optional[float] = Field(
         default_factory=lambda: get_default_sampler_value("typical", 1.0),
@@ -268,6 +272,7 @@ class BaseSamplerRequest(BaseModel):
             "negative_prompt": self.negative_prompt,
             "json_schema": self.json_schema,
             "grammar_string": self.grammar_string,
+            "speculative_ngram": self.speculative_ngram,
         }
 
         return {**gen_params, **kwargs}