add hpke bindings

[tofay]

and refactor the ffi/openssl code

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.82%. Comparing base (ff2af85) to head (69cbc0f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib.rs	0.00%	1 Missing ⚠️
src/openssl_internal/mod.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
+ Coverage   85.79%   85.82%   +0.03%     
==========================================
  Files          12       14       +2     
  Lines        1274     1277       +3     
==========================================
+ Hits         1093     1096       +3     
  Misses        181      181              

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