feat: implement Arkesel SMS provider (Ghana / West Africa) #57

Summary

Implement the Arkesel SMS provider inside src/SmsBridge/Providers/Arkesel/.

Arkesel is a Ghana/West Africa communication provider with OpenAPI documentation for SMS V1, SMS V2, Voice, OTP, USSD, and related APIs. This adds a strong West African provider option beyond Hubtel.

Official docs:

• Developer docs: https://developers.arkesel.com/
• OpenAPI spec: https://developers.arkesel.com/spec/api_spec.v2.3.1.yaml

Files to create

• src/SmsBridge/Providers/Arkesel/ArkeselSmsProvider.cs
• src/SmsBridge/Providers/Arkesel/ArkeselSmsRequestMapper.cs
• src/SmsBridge/Providers/Arkesel/ArkeselSmsResponseMapper.cs
• src/SmsBridge/Options/ArkeselOptions.cs
• Register UseArkesel() in src/SmsBridge/DependencyInjection/SmsBridgeProviderBuilder.cs
• Add HttpClientNames.Arkesel in src/SmsBridge/Internal/Http/HttpClientNames.cs
• Add SmsProviderType.Arkesel to the enum

Arkesel API Details

• Base URL: https://sms.arkesel.com
• SMS V1 send endpoint: GET /sms/api?action=send-sms
• SMS V1 auth: api_key query parameter
• SMS V1 request fields include api_key, to, from, sms, and optional use_case for Nigerian contacts
• SMS V2 uses API key in a header; prefer SMS V2 if its send endpoint is stable and straightforward in the OpenAPI spec
• Response/status docs include:
  • V1 success: OK
  • V1 errors: 100, 101, 102, 103, 104, 105, 106, 109, 111
  • V2 success: 200
  • V2 errors: 401, 402, 403, 422, 500

Options

public sealed class ArkeselOptions
{
    public required string ApiKey { get; init; }
    public required string Sender { get; init; }
    public string? UseCase { get; init; }
    public bool UseSmsV2 { get; init; } = true;
}

Implementation Notes

• Prefer SMS V2 if the send endpoint is confirmed from the spec; otherwise implement V1 first because it is explicitly documented.
• Add use_case support for Nigerian contacts when configured.
• Map accepted response details to SmsSendResult.ProviderMessageId where available; otherwise map success without a provider id.
• Map documented status codes to SMSBridge failure semantics.

Tests to add

• tests/SmsBridge.ProviderTests/ArkeselResponseMapperTests.cs
• tests/SmsBridge.ProviderTests/ArkeselProviderTests.cs

Acceptance Criteria

• Provider sends SMS through Arkesel using IHttpClientFactory
• Provider supports configured sender and optional use_case
• Provider authenticates with configured API key
• Response mapper handles documented V1/V2 success and error codes
• Provider maps Arkesel API failures to failed SmsSendResult
• Transient HTTP failures set IsTransientFailure = true
• UseArkesel() registers the provider in DI
• All tests pass - dotnet test
• dotnet build has 0 warnings