Add registration tests for the validator and composer rule lists

[glen-84]

Summary

• Rule tests inject the rule under test directly, so a rule's own tests stay green when it is dropped from the list that actually runs it. Across the four lists only five of the 97 rules were pinned at all, incidentally, by composer-level tests that assert a specific error code.
• Four tests now assert each registered set in order: SchemaValidator.AddDefaultRules (20 rules), and SchemaComposer's source-schema (37), pre-merge (20), and post-merge (20) lists. Order is part of the assertion because handler dispatch follows registration order.
• To reach the lists, the three composer lists become internal static properties carrying the literal, so there is one member per list rather than a field plus an accessor, and SchemaValidator gains an internal Rules accessor with an InternalsVisibleTo entry for its test project.

Test plan

• Six mutations confirm the tests bite: removing a rule from each of the four lists, adding a duplicate rule, and swapping two adjacent rules in AddDefaultRules.
• Full suites run for Types.Validation (142) and Fusion.Composition (743).

[Copilot]

Pull request overview

This PR strengthens safety around schema validation/composition by adding tests that pin the registered rule lists (and their order), preventing rules from being silently dropped from the real execution pipelines.

Changes:

• Add assertion tests that verify the exact rule registration sets and order for SchemaValidator defaults and SchemaComposer’s source/pre-merge/post-merge rule lists.
• Expose SchemaComposer rule lists as internal static properties so tests can assert the literal registered sequences.
• Add an internal accessor for SchemaValidator’s rules and grant test-assembly access via InternalsVisibleTo.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/HotChocolate/Fusion/test/Fusion.Composition.Tests/SchemaComposerTests.cs	Adds tests asserting the registered composer rule lists and order.
src/HotChocolate/Fusion/src/Fusion.Composition/SchemaComposer.cs	Exposes composer rule lists as internal properties and uses them at call sites.
src/HotChocolate/Core/test/Types.Validation.Tests/SchemaValidatorTests.cs	Adds a test asserting the default schema validator rule registration/order.
src/HotChocolate/Core/src/Types.Validation/SchemaValidator.cs	Adds an internal accessor exposing the validator’s configured rules for tests.
src/HotChocolate/Core/src/Types.Validation/HotChocolate.Types.Validation.csproj	Adds InternalsVisibleTo for the Types.Validation test project.

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[github-actions]

Patch coverage

100.0% of changed lines covered (7/7)

File	Covered	Changed	Patch %
…/HotChocolate/Core/src/Types.Validation/SchemaValidator.cs	1	1	100.0% 🟢
…/HotChocolate/Fusion/src/Fusion.Composition/SchemaComposer.cs	6	6	100.0% 🟢

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Project coverage: 54.4% (242433/445718 lines)