fix: detect in-memory GPG signing credentials for bip32-ed25519 publishing
The signing credential check only looked for signing.keyId property and GPG_KEY_ID env var, missing the in-memory signing properties used by CI (signingInMemoryKey / ORG_GRADLE_PROJECT_signingInMemoryKey). This caused unsigned artifacts to be uploaded to Maven Central, which silently rejects them during validation. Co-Authored-By: Claude Opus 4.6 <[email protected]> Signed-off-by: Yurii Shynbuiev <[email protected]>