Replace errors.New() with ErrInternal()/ErrTimeout() and errors.Unwrap(err)
with err.Unwrap() — the MiningError type provides both without the banned import.
Co-Authored-By: Charon <charon@lethean.io>
Test names lacked the AX-required suffix pattern (RFC-025 §10 test naming).
Renamed all 8 functions to TestErrors_* with _Good, _Bad, and _Ugly suffixes.
Also renamed loop variables from tt to c (predictable name, AX principle 1).
Co-Authored-By: Charon <charon@lethean.io>