Add AuthzClientCryptoProvider for authorization client cryptographic operations

[ShashankFC]

Test 3nnn## Summary by CodeRabbitnn## Release Notesnn* New Featuresn * Enhanced cryptographic support with ECDSA algorithm implementation for authorization client operations.n * Improved crypto provider selection with priority ordering mechanism.nn* Testsn * Added test coverage for ECDSA algorithm variants (ES256, ES384, ES512).nn* Choresn * Added testing framework dependencies.nn_{✏️ Tip: You can customize this high-level summary in your review settings.}nnn---nReplicated from ai-code-review-evaluation/keycloak-coderabbit#3

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Note

Medium Risk
Touches shared crypto provider discovery/selection and adds new signature encoding/decoding logic; failures could impact cryptographic operations at runtime, though changes are relatively contained and backed by targeted tests.

Overview
Adds an AuthzClientCryptoProvider (registered via META-INF/services) and minimal ASN.1 DER encode/decode helpers to support ECDSA signature format conversion (DER ↔ concatenated R/S) in the authz client.

Updates CryptoIntegration/CryptoProvider to allow multiple providers on the classpath by introducing order()-based selection (highest wins) and logging ignored providers, and ensures AuthzClient.create(Configuration) initializes crypto integration. Adds JUnit/Hamcrest test dependencies and a new ECDSAAlgorithmTest covering ES256/ES384/ES512 round-trips.

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[ShashankFC]

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Dead code: unused ASN1Encoder instances in conversion method

Low Severity

Two ASN1Encoder.create().write(...) calls in concatenatedRSToASN1DER create encoder instances, write rBigInteger and sBigInteger to them, then immediately discard the results. The actual encoding happens in the return statement below. These appear to be leftover from an earlier implementation and are dead code that performs unnecessary allocations and I/O.