ffi: succeed with false for revocation-code predicates on live keys

[ronaldtse]

Summary

• rnp_key_is_compromised(), rnp_key_is_retired() and rnp_key_is_superseded() returned RNP_ERROR_BAD_PARAMETERS when the queried key was not revoked, although a key which is not revoked is a normal state rather than a failure. Callers therefore had to map the error code to false by hand and could not distinguish a healthy key from an actual problem, while the sibling predicates rnp_key_is_revoked() and rnp_key_is_valid() already succeed with a boolean for the same state, as reported in rnp_key_is_compromised/retired/superseded return RNP_ERROR_BAD_PARAMETERS for keys that are not revoked #2467.
• The three predicates now succeed with false for a key which is not revoked at all, and RNP_ERROR_BAD_PARAMETERS remains reserved for an invalid key handle.
• The change is a three-line adjustment in the shared rnp_key_is_revoked_with_code() helper, together with a regression test which exercises all three predicates on a non-revoked key inside test_ffi_revocations.

Test plan

• rnp_tests.test_ffi_revocations passes with the new assertions on a non-revoked key
• full CI matrix, which also re-runs the existing assertions for revoked keys on all three predicates

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.46%. Comparing base (26482f6) to head (0dd1359).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2488   +/-   ##
=======================================
  Coverage   85.45%   85.46%           
=======================================
  Files         125      125           
  Lines       23042    23043    +1     
=======================================
+ Hits        19691    19693    +2     
+ Misses       3351     3350    -1     

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