[jwe] Work with non X25519 ECDH encryption

[lestrrat]

fixes #1434

This change introduces conversion from ECDH keys to ECDSA keys such that JWE encryption works for both types of raw keys.

[Copilot]

Pull Request Overview

This PR enables JWE (JSON Web Encryption) to work with non-X25519 ECDH encryption by adding support for ECDH keys using P-256, P-384, and P-521 curves. The implementation introduces a conversion mechanism between ECDH and ECDSA key formats to leverage existing ECDSA encryption functions.

• Adds ECDH to ECDSA key conversion functionality
• Modifies JWE encryption logic to handle ECDH keys for non-X25519 curves
• Includes comprehensive test coverage for the new functionality

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/keyconv/keyconv.go	Implements ECDHToECDSA conversion function and curve mapping utilities
internal/keyconv/keyconv_test.go	Adds comprehensive tests for ECDH to ECDSA conversion functionality
jwe/encrypt.go	Updates encryption logic to handle ECDH keys by converting to ECDSA when needed
jwe/jwe_test.go	Adds basic test for ECDH key encryption/decryption
jwx_test.go	Adds comprehensive interoperability tests with jose for different ECDH curves

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