Why make this change?

Closes #3462

What is this change?

Refactors how SQL Find responses signal pagination so it no longer relies on the JSON shape of the result list.

Previously, SqlResponseHelpers.FormatFindResult appended pagination metadata to the row collection as an in-band sentinel a single-element JSON array wrapping { "nextLink": ... } (REST) or { "after": ... } (MCP) and OkResponse recovered it by checking whether the last element of the result list was a JsonValueKind.Array. This worked only because SQL backends never produced array-shaped row values.

That assumption breaks with SQL Server's JSON type, JSON_ARRAY(), vector, and other collection-shaped column values a real data row could carry an array-shaped tail value and be misclassified as a pagination envelope.

This change carries pagination metadata out-of-band:

• FormatFindResult builds the response envelope directly as a typed projection ({ value, nextLink } for REST, { value, after } for MCP) using a bool hasNext local instead of encoding the decision into the row collection.
• OkResponse(JsonElement, bool?) is reduced to a single-responsibility envelope wrapper. The signature is preserved (isMcpRequest is now optional and accepted-but-unused) so existing callers of Microsoft.DataApiBuilder.Core continue to compile and link unchanged. The shape-detection branch is removed from the body.
• GetConsolidatedNextLinkForPagination is preserved with its original signature and JsonElement return type for source compatibility. Internally, FormatFindResult now constructs the next-page URL inline (it needs the URL as a string to put into the typed response envelope), avoiding a serialize-then-parse round-trip just to satisfy the old wrapper shape.
• DetermineExtraFieldsInResponse gains a JsonValueKind.Object guard so future array/scalar/collection-typed row shapes return an empty extra-fields set rather than throwing on EnumerateObject().
• Drive-by cleanup: removed a dead ! null-forgiving operator, standardized JsonValueKind checks on is, refreshed stale comments and XML docs, removed dead commented-out code.

Wire format is unchanged for both REST and MCP. Public API surface is byte-identical to main no signatures added, removed, or renamed; no [Obsolete] warnings emitted to downstream consumers. The new gate:

bool hasNext = isCollection && SqlPaginationUtil.HasNext(...)

is logically equivalent to the original gate.

How was this tested?

Added seven focused unit tests in SqlResponseHelpersUnitTests.cs pinning the envelope shape across every branch:

1. Empty result
2. Single object
3. Collection without next page
4. Collection with next page (REST → nextLink)
5. Collection with next page (MCP → after)
6. Round-trip of a row containing an array-valued column (forward-looking coverage for SQL Server JSON/vector column shapes)
7. Regression guard for the actual pre-refactor failure mode: a result whose last top-level element is itself a JSON array the exact trigger the old in-band sentinel detection used is now correctly preserved as ordinary data instead of being unpacked as a pagination envelope.

All seven pass. dotnet format --verify-no-changes is clean across the touched files.