feat(ai): add ai gateway provider methods support

[innomaxx]

Closes #359

[Copilot]

Pull request overview

Adds SDK support for the Crowdin AI Gateway provider methods (GET/POST/PUT/PATCH/DELETE) so consumers can manage provider gateway configuration through the .NET client.

Changes:

• Introduces IAiGatewayApiExecutor and AiGatewayApiExecutor to call AI Gateway endpoints and return raw JObject responses.
• Exposes AI-related executors on ICrowdinApiClient / CrowdinApiClient via new AI and AiGateway properties.
• Adds unit tests covering the new gateway executor methods.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Crowdin.Api.UnitTesting/Tests/AI/AiGatewayTests.cs	Adds unit tests validating request routing for AI Gateway methods.
src/Crowdin.Api/ICrowdinApiClient.cs	Exposes new AI executors on the public client interface.
src/Crowdin.Api/CrowdinApiClient.cs	Instantiates and exposes AI and AiGateway executors on the concrete client.
src/Crowdin.Api/AI/Gateway/IAiGatewayApiExecutor.cs	Defines the AI Gateway executor contract (GET/POST/PUT/PATCH/DELETE).
src/Crowdin.Api/AI/Gateway/AiGatewayApiExecutor.cs	Implements the AI Gateway calls and URL formation logic.

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[Copilot]

AiGatewayApiExecutor stores _jsonParser (and has a ctor overload that accepts it) but never uses it anywhere in the class. This leaves dead code and will produce an unused-field warning; consider removing _jsonParser and the (ICrowdinApiClient, IJsonParser) constructor, or add typed Execute*<T>() methods that actually use the parser.

Suggested change

	private readonly IJsonParser _jsonParser;
	public AiGatewayApiExecutor(ICrowdinApiClient apiClient)
	{
	_apiClient = apiClient;
	_jsonParser = apiClient.DefaultJsonParser;
	}
	public AiGatewayApiExecutor(ICrowdinApiClient apiClient, IJsonParser jsonParser)
	{
	_apiClient = apiClient;
	_jsonParser = jsonParser;
	}
	public AiGatewayApiExecutor(ICrowdinApiClient apiClient)
	{
	_apiClient = apiClient;
	}

[Copilot]

Adding new members to ICrowdinApiClient (AI / AiGateway) is a binary breaking change for any external implementations of this public interface. If backwards compatibility is a goal, consider exposing these executors only on CrowdinApiClient (or via a separate interface/extension methods), or ensure the package versioning reflects this breaking API change.

Suggested change

	// ReSharper disable once InconsistentNaming
	IAiApiExecutor AI { get; }
	IAiGatewayApiExecutor AiGateway { get; }