aes-gcm internals: Use `cpu_features` from GCM context.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (244627f) 96.23% compared to head (3cb3965) 96.22%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1948 +/- ## ========================================== - Coverage 96.23% 96.22% -0.02% ========================================== Files 135 135 Lines 20632 20617 -15 Branches 226 226 ========================================== - Hits 19855 19838 -17 Misses 743 743 - Partials 34 36 +2 ```

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