feat: StreamPaged<T> - stream a paged JSON envelope in a single round-trip (fixes #5009)

[erdtsieck]

Summary

Adds a new StreamPaged<T> result type to Marten.AspNetCore that streams a paged list of documents plus paging metadata as a single JSON envelope directly to the HTTP response, in one database round trip:

{"pageNumber":3,"pageSize":25,"totalItemCount":1207,"pageCount":49,"hasNextPage":true,"hasPreviousPage":true,"items":[...]}

Closes #5009.

Implementation

• Marten.Linq.MartenLinqQueryable<T>.StreamPagedJsonArray - sets Statistics, applies Skip/Take, delegates to the provider.
• MartenLinqQueryProvider.StreamPagedMany - builds the LINQ statement/command (which includes count(*) OVER() as total_rows via LinqConstants.StatsColumn when Statistics is set), then executes via the session.
• QuerySession.StreamPagedMany + JsonStreamingExtensions.StreamPagedMany - reads total_rows from the first row of the DbDataReader, computes pageCount/hasNextPage/hasPreviousPage (mirroring PagedList.ProcessResults), writes the envelope prefix, then streams each row's raw document JSON straight into the items array without deserializing/reserializing documents.
• QueryableExtensions.StreamPagedJsonArray<T> (Marten core) - public entry point exposing the above.
• Marten.AspNetCore.QueryableExtensions.WritePaged<T> + StreamPaged<T> (IResult + IEndpointMetadataProvider, mirroring StreamMany<T>) - the minimal-API/Wolverine.Http-facing wrapper.

Zero-row result sets produce totalItemCount: 0, pageCount: 0, and an empty items array (count(*) OVER() is not present on any row when nothing matches).

Tests

• src/DocumentDbTests/Reading/Json/streaming_json_results.cs - 8 new [Fact]s covering first/middle/last/single page, no-hits, and argument validation (pageNumber < 1, pageSize < 1). All passing.
• src/Marten.AspNetCore.Testing/stream_paged_tests.cs (new) - Alba HTTP-level tests against a new /minimal/issues/paged/{pageNumber}/{pageSize} endpoint added to IssueService.

Docs

• docs/documents/querying/linq/paging.md - new "Streaming a Paged JSON Envelope" section describing StreamPagedJsonArray<T>().
• docs/documents/aspnetcore.md - added StreamPaged<T> to the typed streaming result types table and a full usage subsection.
• Verified clean with markdownlint-cli (--disable MD009) and cspell against docs/**/*.md.

Test status

• DocumentDbTests (both net9.0 and net10.0, run individually): all 8 new stream_paged_json_array_* tests pass.
• Marten.AspNetCore.Testing: the whole suite (including pre-existing streaming_result_types_tests) currently fails to boot the Alba test host on this branch's base commit due to an unrelated, pre-existing environment issue (InvalidProjectionException: No source-generated dispatcher found for SingleStreamProjection<Order, Guid>). Verified this failure is not caused by this change - it reproduces identically on a clean, unmodified checkout of master.

Notes

• Running the two test TFMs (net9.0/net10.0) together via dotnet test in parallel against the same shared Postgres schema can cause cross-run data contention/deadlocks unrelated to this feature; running each TFM individually avoids this and both pass cleanly.