feat(csharp): expose metadata on paginated responses

[patrickthornton]

Description

Equivalent of #10629 in C#.

Added three new properties to Page<TItem>:

• Response (object?), the full deserialized API response object
• StatusCode (HttpStatusCode), the HTTP status code
• Headers (ResponseHeaders?), the HTTP response headers

Pager now explicitly calls .WithRawResponse() so Page can have Response. There was a somewhat suboptimal design decision made here to avoid a breaking change; namely, I'd rather have expanded the interface of Pager to Pager<TResponse, TItem> so users wouldn't have to cast Response to the correct type to use it, but that would break any code that implemented the interface. I'd theoretically be alright with this since getting the raw response here is a relatively fringe use case compared to the status code or headers, but it's still a compromise.

Code example:

  var pager = await client.Users.ListAsync(request);
  await foreach (var page in pager.AsPagesAsync())
  {
      // HTTP metadata
      Console.WriteLine(page.StatusCode);   // e.g., HttpStatusCode.OK
      Console.WriteLine(page.Headers);      // ResponseHeaders

      // Full response (cast to access non-item fields)
      var response = (ListUsersPaginationResponse)page.Response!;
      Console.WriteLine(response.TotalCount);
  }

Testing

Regeneration of all pagination fixtures.

• Unit tests added/updated
• Manual testing completed

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SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-08T04:49:09Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
csharp-sdk	square	132s	171s	126s	-6s (-4.5%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-04-08T04:49:09Z). Trigger benchmark-baseline to refresh.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-08T04:49:09Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
csharp-sdk	square	132s	171s	132s	+0s (+0.0%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-04-08T04:49:09Z). Trigger benchmark-baseline to refresh.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against latest nightly baseline on main (2026-04-09T04:46:50Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
csharp-sdk	square	95s	138s	92s	-3s (-3.2%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-04-09T04:46:50Z). Trigger benchmark-baseline to refresh.