Set generation config defaults according to decoding method

[mzegla]

No description provided.

[Copilot]

Pull Request Overview

This PR implements automatic default parameter setting for assisted decoding methods (Speculative Decoding and Prompt Lookup) when parameters are not explicitly provided in requests. Previously, missing parameters caused execution errors; now, sensible defaults are applied based on the detected decoding method.

Key changes:

• Added DecodingMethod enum and automatic detection logic to identify pipeline configuration (standard, speculative decoding, or prompt lookup)
• Implemented adjustConfigForDecodingMethod() to set default values (num_assistant_tokens=5, max_ngram_size=3) when parameters are missing
• Updated tests to verify that missing parameters now result in successful execution with defaults instead of errors

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/llm/io_processing/base_generation_config_builder.hpp	Added DecodingMethod enum and adjustConfigForDecodingMethod() method declaration
src/llm/io_processing/base_generation_config_builder.cpp	Implemented default parameter logic for different decoding methods
src/llm/io_processing/generation_config_builder.hpp	Updated constructor signature and added method to adjust config for decoding method
src/llm/servable.hpp	Added decodingMethod field and determineDecodingMethod() method declaration
src/llm/servable.cpp	Implemented decoding method detection based on plugin configuration
src/llm/servable_initializer.cpp	Added call to determine decoding method during servable initialization
src/llm/language_model/legacy/servable.cpp	Updated to pass decoding method and call adjustment method
src/llm/visual_language_model/legacy/servable.cpp	Updated to pass decoding method and call adjustment method
src/llm/io_processing/llama3/generation_config_builder.hpp	Updated constructor to accept decoding method parameter
src/llm/io_processing/hermes3/generation_config_builder.hpp	Updated constructor to accept decoding method parameter
src/llm/io_processing/phi4/generation_config_builder.hpp	Updated constructor to accept decoding method parameter
src/test/llm/assisted_decoding_test.cpp	Added tests for default parameter behavior and updated expectations from error to success
docs/model_server_rest_api_chat.md	Documented default parameter values for assisted decoding methods

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