Refactor low-level crypto to C++ style.

[ni4]

This is rather huge PR, which would do simple things:

• avoid plain C structs and functions by replacing those with C++ classes/methods
• use references instead of pointers
• avoid static fixed-size buffer in favor of std::vector
• use C++ wrappers with destructors for proper Botan/OpenSSL objects deallocation.

[codecov]

Codecov Report

Attention: Patch coverage is 85.69528% with 215 lines in your changes missing coverage. Please review.

Project coverage is 84.88%. Comparing base (ddcbaa9) to head (858ad09).
Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/crypto/sm2.cpp	77.67%	25 Missing ⚠️
src/lib/crypto/elgamal.cpp	77.50%	18 Missing ⚠️
src/lib/crypto/rsa_ossl.cpp	88.75%	18 Missing ⚠️
src/lib/crypto/dsa.cpp	81.39%	16 Missing ⚠️
src/lib/crypto/dsa_ossl.cpp	84.15%	16 Missing ⚠️
src/lib/crypto/ecdh.cpp	84.94%	14 Missing ⚠️
src/lib/crypto/ossl_utils.hpp	82.05%	14 Missing ⚠️
src/lib/crypto/rsa.cpp	86.86%	13 Missing ⚠️
src/lib/crypto/ec.cpp	75.55%	11 Missing ⚠️
src/lib/crypto/ecdsa_ossl.cpp	73.80%	11 Missing ⚠️
... and 11 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2292      +/-   ##
==========================================
+ Coverage   84.81%   84.88%   +0.06%     
==========================================
  Files         116      114       -2     
  Lines       23346    22783     -563     
==========================================
- Hits        19802    19339     -463     
+ Misses       3544     3444     -100     

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[desvxx]

We can't have exception here anymore?

[ni4]

We don't need to handle it here and now allow to pass it up. Check was added during initial transition from C to C++, when FFI didn't handle exceptions or something like that.

[maxirmx]

1. IMHO wrappers in botan_utils.hpp and ossl_utils.hpp look like derivatives of unique_ptr with custom Deleter
   I am not at all saying that it shall be changed, just noting that it is a kind of reimplementation of standard library

2. Purists would say that in the newer files nullptr shall be used and not NULL

[ni4]

@maxirmx

1. IMHO wrappers in botan_utils.hpp and ossl_utils.hpp look like derivatives of unique_ptr with custom Deleter
   I am not at all saying that it shall be changed, just noting that it is a kind of reimplementation of standard library

Thanks for this suggestion! Somehow I missed the idea to use unique_ptr with custom deleter, with it it looks much better and cleaner, so updated the code.

2. Purists would say that in the newer files `nullptr` shall be used and not `NULL`

Agree, missed this as well, updated code fore C++ return types.

[maxirmx]

macos-12 GHA runner is not available anymore
I have changed it to macos-13, thought it was faster tne making a comment

[ni4]

@maxirmx Is this good to merge now?