Adopt pageable spector scenarios

[JoshLove-msft]

Fixes #48061

[Copilot]

Pull Request Overview

This PR updates the generated pageable patterns to support Spector’s next-link and continuation-token scenarios by passing explicit nextLink URIs, unifying loop logic, and propagating cancellation tokens to the base Pageable constructors.

• Constructors now call the base Pageable ctor with the cancellation token.
• Paging methods switch from string-based continuation tokens to Uri next-link variables and reshape loops accordingly.
• The code generator (CollectionResultDefinition) was refactored to better handle protocol vs. model-based paging, plus adjustments to launch settings and script exclusions.

Reviewed Changes

Copilot reviewed 54 out of 54 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/Providers/.../NextLinkTests/*.cs	Updated test stubs to use Uri nextLink and new loop patterns
test/Providers/.../ListPageableTests/*.cs	Converted single-page loops to direct calls, removed do/while
test/Providers/.../ContinuationTokenTests/*.cs	Switched to nextPage tokens, removed old continuationToken logic
src/Providers/CollectionResultDefinition.cs	Refactored generator to insert nextLink, nullability, and loop building
src/Properties/launchSettings.json	Added http-payload-pageable profile
eng/scripts/Generate.ps1	Removed failing payload/pageable spec from generation script

Comments suppressed due to low confidence (1)

eng/packages/http-client-csharp/generator/Azure.Generator/src/Providers/CollectionResultDefinition.cs:45

• The continuationToken parameter should remain nullable to reflect that callers may pass null. Use new CSharpType(typeof(string), isNullable: true) so the generated signature is string? continuationToken.

private static readonly ParameterProvider ContinuationTokenParameter = new("continuationToken", "A continuation token indicating where to resume paging.", new CSharpType(typeof(string)));