feat: implement BulkSMSNigeria SMS provider (Nigeria)

[teesofttech]

Summary

Implement the BulkSMSNigeria SMS provider inside src/SmsBridge/Providers/BulkSmsNigeria/.

BulkSMSNigeria is a Nigeria-focused SMS gateway with a documented REST API, DND delivery support, delivery reports, sender IDs, and a sandbox endpoint. This adds stronger local Nigerian coverage beyond Termii and SmartSMSSolutions.

Official docs:

• API docs: https://www.bulksmsnigeria.com/api
• Sandbox docs: https://www.bulksmsnigeria.com/api

Files to create

• src/SmsBridge/Providers/BulkSmsNigeria/BulkSmsNigeriaSmsProvider.cs
• src/SmsBridge/Providers/BulkSmsNigeria/BulkSmsNigeriaSmsRequestMapper.cs
• src/SmsBridge/Providers/BulkSmsNigeria/BulkSmsNigeriaSmsResponseMapper.cs
• src/SmsBridge/Options/BulkSmsNigeriaOptions.cs
• Register UseBulkSmsNigeria() in src/SmsBridge/DependencyInjection/SmsBridgeProviderBuilder.cs
• Add HttpClientNames.BulkSmsNigeria in src/SmsBridge/Internal/Http/HttpClientNames.cs
• Add SmsProviderType.BulkSmsNigeria to the enum

BulkSMSNigeria API Details

• Production base URL: https://www.bulksmsnigeria.com/api/v2
• Sandbox base URL: https://www.bulksmsnigeria.com/api/sandbox/v2
• Send endpoint: POST /sms
• Auth: Authorization: Bearer {ApiToken}
• Request (JSON):

  {
    "from": "SMSBridge",
    "to": "2348012345678",
    "body": "Hello from SMSBridge",
    "gateway": "direct-refund",
    "callback_url": "https://example.com/sms/callback"
  }

• Response fields documented include status, code, message, data.message_id, cost, currency, recipients_count, and gateway_used.

Options

public sealed class BulkSmsNigeriaOptions
{
    public required string ApiToken { get; init; }
    public required string From { get; init; }
    public string? Gateway { get; init; }
    public string? CallbackUrl { get; init; }
    public bool UseSandbox { get; init; }
}

Implementation Notes

• Prefer JSON request/response handling.
• Use the sandbox base URL when UseSandbox is enabled.
• Map data.message_id to SmsSendResult.ProviderMessageId.
• Treat non-success status/code values as failed sends.
• Preserve gateway_used, cost, and currency in provider metadata if SMSBridge supports metadata for send results.

Tests to add

• tests/SmsBridge.ProviderTests/BulkSmsNigeriaResponseMapperTests.cs
• tests/SmsBridge.ProviderTests/BulkSmsNigeriaProviderTests.cs

Acceptance Criteria

• Provider sends via /sms using IHttpClientFactory
• Provider supports production and sandbox base URLs
• Request mapper emits from, to, body, optional gateway, and optional callback_url
• Response mapper maps data.message_id to SmsSendResult.ProviderMessageId
• Provider maps failed BulkSMSNigeria responses to failed SmsSendResult
• Transient HTTP failures set IsTransientFailure = true
• UseBulkSmsNigeria() registers the provider in DI
• All tests pass - dotnet test
• dotnet build has 0 warnings