tools, test: Fix missing NULL checks after malloc

[hyperfinitism]

This PR fixes several places where malloc() return values were used without a NULL check. The changes are split into two commits to keep the review straightforward:

1. tools/: production code fixes (add missing NULL checks and OOM handling)
   • tpm2_duplicate.c
   • tpm2_encryptdecrypt.c
   • tpm2_getekcertificate.c
   • tpm2_nvreadpublic.c
   • tpm2_verifysignature.c
2. test/unit/: test fixes (add assert_non_null after malloc())
   • test_tpm2_auth_util.c
   • test_tpm2_session.c