Extract common YAML parsing helpers to a shared utility header to reduce code duplication and improve consistency

[mfaferek93]

Summary

Extract common YAML parsing helpers to a shared utility header to reduce code duplication and improve consistency.

Currently we have YAML parsing helpers in two places:

• correlation/config_parser.cpp - get_string(), get_bool(), get_uint32(), get_double()
• fault_manager_node.cpp - raw YAML::Node access for snapshot config

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Proposed solution (optional)

Create include/ros2_medkit_fault_manager/yaml_utils.hpp with:

namespace ros2_medkit_fault_manager::yaml_utils {
  std::string get_string(const YAML::Node&, const std::string& key, const std::string& default_value = "");
  bool get_bool(const YAML::Node&, const std::string& key, bool default_value = false);
  uint32_t get_uint32(const YAML::Node&, const std::string& key, uint32_t default_value = 0);
  double get_double(const YAML::Node&, const std::string& key, double default_value = 0.0);
}

Then refactor:

1. config_parser.cpp - use shared utils
2. fault_manager_node.cpp (load_snapshot_config_from_yaml) - use shared utils

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Additional context (optional)

Originated from code review discussion: #121 (comment)