Back propagate errors from OpenSSL

[maxtropets]

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[Copilot]

Pull request overview

This PR improves diagnostics by propagating human-readable OpenSSL error-queue details through signing, verification, and key (de)serialization paths, and updates/adds tests to assert on those error strings.

Changes:

• Add ossl_err_string() helper and include OpenSSL error details in many Err(String) returns across wrappers/sign/verify.
• Update COSE, sign, verify, and key import tests to assert on specific propagated error messages/details.
• Refine error messages to include the OpenSSL function name and return code.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/verify.rs	Adds OpenSSL error-queue detail to verify failures and introduces verify behavior tests.
src/sign.rs	Adds OpenSSL error-queue detail to signing failures and introduces sign behavior tests.
src/ossl_wrappers.rs	Introduces ossl_err_string() and threads OpenSSL error detail through key/context/ecdsa conversion errors; expands tests.
src/cose.rs	Tightens negative tests to assert exact error strings and adds error-propagation tests through COSE APIs.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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