Add [RegisterServices] support

[viceroypenguin]

No description provided.

[Copilot]

Pull request overview

Adds support for [RegisterServices]-annotated methods so consumers can plug custom registration logic into the generated Add{Assembly}Services(...) extension method, with an analyzer enforcing the required method signature and new tests/snapshots validating output.

Changes:

• Extend the incremental generator pipeline to discover [RegisterServices] methods and emit II.RegisterServicesMethods.g.cs that invokes them.
• Add RegisterServicesMethodAnalyzer (INJ0001) to enforce valid [RegisterServices] method signatures.
• Add generator/analyzer tests and verified snapshots for the new generated output.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/Immediate.Injections.Tests/Utility.cs	Adds metadata reference for RegisterServicesAttribute so test compilations can bind the attribute.
tests/Immediate.Injections.Tests/GeneratorTests/RegisterServicesTests.cs	New generator tests validating RegisterServices method discovery and invocation in generated output.
tests/Immediate.Injections.Tests/GeneratorTests/GeneratorTestHelper.cs	Updates tracked incremental steps list to include RegisterServicesMethods.
tests/Immediate.Injections.Tests/AnalyzerTests/RegisterServicesMethodAnalyzerTests.cs	New analyzer tests validating INJ0001 triggers/doesn’t trigger correctly.
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodWhenLangVersionIs12#II.ServiceCollectionExtensions.g.verified.cs	Snapshot for generated service collection extensions when language version is C# 12.
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodWhenLangVersionIs12#II.RegisterServicesMethods.g.verified.cs	Snapshot for generated RegisterServices implementation (C# 12 scenario).
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodIsCalled1#II.ServiceCollectionExtensions.g.verified.cs	Snapshot for generated extensions (default language version) calling RegisterServices.
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodIsCalled1#II.RegisterServicesMethods.g.verified.cs	Snapshot for generated RegisterServices implementation calling a services-only method.
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodIsCalled2#II.ServiceCollectionExtensions.g.verified.cs	Snapshot for generated extensions with params ReadOnlySpan<string> tags.
tests/Immediate.Injections.Tests/GeneratorTests/Snapshots/RegisterServicesTests.ValidRegisterServicesMethodIsCalled2#II.RegisterServicesMethods.g.verified.cs	Snapshot for generated RegisterServices implementation calling a (services, tags) method.
src/Immediate.Injections.Generators/ImmediateInjectionsGenerator.cs	Adds a new syntax provider pipeline for [RegisterServices] methods and wires rendering.
src/Immediate.Injections.Generators/ImmediateInjectionsGenerator.Transform.cs	Adds transformation to RegisterServicesMethod model including fully-qualified callable name and whether it takes tags.
src/Immediate.Injections.Generators/ImmediateInjectionsGenerator.Render.cs	Adds rendering path for II.RegisterServicesMethods.g.cs via a new Scriban template.
src/Immediate.Injections.Generators/ImmediateInjectionsGenerator.Models.cs	Adds RegisterServicesMethod model record for template rendering.
src/Immediate.Injections.Generators/Templates/RegisterServices.sbntxt	New template that emits RegisterServices(...) implementation invoking discovered methods.
src/Immediate.Injections.Generators/DisplayNameFormatters.cs	Adds a symbol display format used to generate callable method names.
src/Immediate.Injections.Analyzers/RegisterServicesMethodAnalyzer.cs	New analyzer rule INJ0001 enforcing [RegisterServices] method signature constraints.
src/Immediate.Injections.Analyzers/DiagnosticIds.cs	Adds INJ0001 diagnostic id constant.
src/Immediate.Injections.Analyzers/AnalyzerReleases.Unshipped.md	Documents the new analyzer rule.
src/Common/Utility.cs	Adds WhereNotNull for IncrementalValuesProvider<T?>.
src/Common/ITypeSymbolExtensions.cs	Adds extension members to validate method signatures and identify relevant symbols/namespaces.

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