Update Composite ML-DSA import/export APIs

[PranavSenthilnathan]

Closes #118320

[Copilot]

Pull Request Overview

This PR refactors the Composite ML-DSA import/export APIs to replace the Try*Core pattern with direct export methods that return byte counts instead of boolean success indicators. The change simplifies the API design by moving error handling logic out of the core methods.

Key changes include:

• Changed core export methods from returning bool with out int bytesWritten to returning int directly
• Introduced new overloads that export directly to Span<byte> destinations
• Refactored size validation logic to use min/max bounds instead of complex size range objects
• Updated test infrastructure to match the new API patterns

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Security.Cryptography/ref/System.Security.Cryptography.cs	Added new export overloads and updated abstract method signatures
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/CompositeMLDsaImplementation.*.cs	Updated platform-specific implementations to use new export signatures
src/libraries/Common/src/System/Security/Cryptography/CompositeMLDsaManaged.cs	Refactored managed implementation to use direct return values instead of out parameters
src/libraries/Common/src/System/Security/Cryptography/CompositeMLDsaAlgorithm.cs	Replaced complex SizeRange system with simple min/max bounds and validation methods
src/libraries/Common/src/System/Security/Cryptography/CompositeMLDsa.cs	Updated export methods to use new core APIs and added Span-based overloads
src/libraries/Common/src/System/Security/Cryptography/CryptoPool.cs	Added IsRented property for conditional buffer management
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLDsa/*.cs	Updated tests to match new API patterns and added comprehensive test coverage

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[PranavSenthilnathan]

/cc @jeffhandley @artl93 Updating PQC APIs for RC1 based on API Review approval