Scaffold SLH-DSA based on ML-DSA

[PranavSenthilnathan]

Moslty copied from SLH-DSA with algorithm name, oid, parameters updated for SLH-DSA based on FIPS 205.

Notes:

• Unlike FIPS 204 (ML-DSA) which allows the seed to be exported, FIPS 205 does not allow any internal state to be exported. However, this PR does expose an export method for parity with the ML-DSA implementation.
• Seed size is dependent on the parameter set

I expect that the ML-DSA skeleton might change as work on the implementation progresses, but it's still a useful reference for SLH-DSA in order to have some APIs to start writing tests against.

Progress towards #113506

[Copilot]

Pull Request Overview

This PR scaffolds SLH-DSA based on ML-DSA by introducing new algorithm identifiers, implementation stubs, and corresponding OID definitions.

• Added a new SLHDsaAlgorithm class with static properties for each SLH-DSA variant.
• Introduced platform-specific stub implementations in SLHDsaImplementation.Windows.cs and SLHDsaImplementation.NotSupported.cs.
• Extended the Oids class with SLH-DSA specific OIDs.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/Common/src/System/Security/Cryptography/SLHDsaAlgorithm.cs	Added algorithm identifiers for SLH-DSA.
src/libraries/Common/src/System/Security/Cryptography/SLHDsaImplementation.Windows.cs	Provided Windows-specific stub implementations throwing PlatformNotSupportedException.
src/libraries/Common/src/System/Security/Cryptography/SLHDsaImplementation.NotSupported.cs	Provided fallback stub implementations throwing PlatformNotSupportedException.
src/libraries/Common/src/System/Security/Cryptography/SLHDsaImplementation.cs	Defined the core SLHDsa implementation scaffolding.
src/libraries/Common/src/System/Security/Cryptography/Oids.cs	Extended OID definitions with SLH-DSA specific values.

Comments suppressed due to low confidence (1)

src/libraries/Common/src/System/Security/Cryptography/SLHDsaImplementation.cs:21

• There is an inconsistency in referencing the ParameterSetInfo type: some implementations qualify it as SLHDsa.ParameterSetInfo while others do not. Consider using a consistent reference (either fully qualified or unqualified) across all implementations.

internal static partial SLHDsa ImportPublicKey(ParameterSetInfo info, ReadOnlySpan<byte> source);

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