fix: context length for model import

[vansangpfiev]

Describe Your Changes

This pull request includes several changes to the engine/config/gguf_parser.cc and engine/services/model_service.cc files to improve the handling of model configuration and metadata. The most important changes are grouped by theme below:

Code Simplification and Cleanup:

• Moved the #include <filesystem> directive to the correct position in engine/config/gguf_parser.cc to maintain proper alphabetical order of includes.

Error Handling:

• Reformatted the error message in the ReadString method to improve readability.

Model Configuration:

• Simplified the assignment of max_tokens and ctx_len in the ModelConfigFromMetadata method to directly use max_tokens instead of applying a minimum function.
• Added the assignment of max_tokens to the JSON data in the StartModel method to ensure it is included in the model configuration. [1] [2]

Fixes Issues

• Closes #
• Closes #

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (for bug fixes / features)
• Created issues for follow-up changes or refactoring needed