feat: POWER-4533 - Add support for integrating with Get Latest Icing endpoint in External API

[sarahsa]

Changes:

• Add support for Get Latest Icing Endpoint in External API
• Move DTOs in Grid Insights into separate folder

[Copilot]

Pull request overview

This PR adds integration support for the External API's "Get Latest Icing" endpoint, enabling clients to retrieve recent icing measurements for transmission lines. The changes also refactor existing DTOs by relocating them into a dedicated Dtos subfolder for better organization.

Changes:

• Added GetLatestIcingAsync method to the API client with support for unit system selection and optional time filtering
• Created comprehensive DTO structure for icing data including maximum values and per-span/phase measurements
• Reorganized existing CurrentDto and ConductorTemperatureDto into a separate Dtos folder

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Program.cs	Added example usage demonstrating the new icing endpoint
UrlBuilder.cs	Added URL construction for the icing endpoint with query parameter support
HeimdallApiClient.cs	Implemented GetLatestIcingAsync method with documentation
LatestIcingResponse.cs	Created response wrapper containing icing measurements
LatestCurrentResponse.cs	Updated namespace import for relocated DTOs
LatestConductorTemperatureResponse.cs	Updated namespace import for relocated DTOs
SpanPhaseMeasurementResult.cs	Created DTO for individual span phase measurement with timestamp and unit
SpanPhaseIcingDto.cs	Created DTO for span phase icing data including ice weight, tension, and safety metrics
SpanIcingDto.cs	Created DTO for span-level icing data containing collection of span phases
MeasurementResult.cs	Created base DTO for measurement values with units
MaxIcingDto.cs	Created DTO for maximum icing values across all span phases
IcingDto.cs	Created root DTO containing maximum values and span collection
CurrentDto.cs	Moved to Dtos namespace folder
ConductorTemperatureDto.cs	Moved to Dtos namespace folder

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