Add more test cases

[hug-dev]

• Add a test making a request to a provider that is not registered, check for ProviderNotRegistered error code
• Use a crate that does both hashing and signing/verifying and use it as another client. Both the Parsec client and the Rust one could be used to sign/verify each other computations

[ionut-arm]

• Write an "all providers" test where you go through all possible combinations of crypto provider pairs and:

• create a key in each of the two providers
• sign a random hash with both keys
• export the public keys
• cross-import the public keys
• cross-verify the signature

[ionut-arm]

I'll write down here other ideas I get for tests.

• Go through all config values and decide which ones would benefit from a test.
• Move (TPM provider) integration tests to E2E tests
• Expand stress test to cover new mechanisms (asym encryption) and primitives (elliptic curve algorithms)
• Test what happens when the authenticator in the request header doesn't exist or isn't registered
• Add more sanity testing around the software verify/encrypt in PKCS11
• Expand tests that use is_operation_supported to verify that PsaErrorNotSupported is returned when the opcode isn't listed

[ionut-arm]

Done in #253