refactor: move context struct out of controllers

[louis-jan]

Problem
These context structs are not relevant to the controllers.

struct whisper_server_context {
  whisper_params params;
  whisper_params default_params;
  std::mutex whisper_mutex;
  std::string model_id;

  struct whisper_context_params cparams;
  struct whisper_context* ctx = nullptr;

  whisper_server_context() = default;  // add this line

  // Constructor
  whisper_server_context(const std::string& model_id) {
    this->model_id = model_id;
    this->cparams = whisper_context_params();
    this->ctx = nullptr;
    // store default params so we can reset after each inference request
    this->default_params = whisper_params();
    this->params = whisper_params();
  }

  // Move constructor
  whisper_server_context(whisper_server_context&& other) noexcept
      : params(std::move(other.params)),
        default_params(std::move(other.default_params)),
        whisper_mutex()  // std::mutex is not movable, so we initialize a new one
        ,
        model_id(std::move(other.model_id)),
        cparams(std::move(other.cparams)),
        ctx(std::exchange(
            other.ctx,
            nullptr))  // ctx is a raw pointer, so we use std::exchange
  {}

  bool load_model(std::string& model_path);

  std::string inference(std::string& input_file_path, std::string languague,
                        std::string prompt, std::string response_format,
                        float temperature, bool translate);

  ~whisper_server_context();
};

using namespace drogon;

namespace audio {
class whisperCPP : public drogon::HttpController<whisperCPP>,
                   public BaseModel,
                   public BaseAudio {

Success Criteria
Move to /context folder

Additional context
Add any other context or screenshots about the feature request here.