Add unit test for wolfSSH_RsaVerify

[yosuke-wolfssl]

This PR adds a test that calls wolfSSH_RsaVerify with a signature whose decoded digest content is intentionally wrong (correct size, wrong bytes) and verifies that WS_RSA_E is returned.
Also, this adds the test helper in src/internal.c with WOLFSSH_TEST_INTERNAL guard because wolfSSH_RsaVerify() is hidden in internal.c.

[Copilot]

Pull request overview

Adds an internal unit test to ensure wolfSSH_RsaVerify() fails (returns WS_RSA_E) when the decoded signature digest has the correct size but incorrect contents, using a WOLFSSH_TEST_INTERNAL wrapper since wolfSSH_RsaVerify() is internal-only.

Changes:

• Expose wolfSSH_TestRsaVerify() under WOLFSSH_TEST_INTERNAL (and !WOLFSSH_NO_RSA) for unit testing.
• Add a new unit test test_RsaVerify_BadDigest() that signs a correct DigestInfo and verifies failure when the expected DigestInfo is tampered.
• Add required wolfCrypt RSA/ASN includes for the new unit test.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
wolfssh/internal.h	Declares the internal-test wrapper wolfSSH_TestRsaVerify() behind WOLFSSH_TEST_INTERNAL.
tests/unit.c	Adds RSA verify negative/positive test coverage using a fixed RSA key and tampered DigestInfo.
src/internal.c	Implements wolfSSH_TestRsaVerify() wrapper calling wolfSSH_RsaVerify() with a fixed loc string.

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