fix compilation errors on Windows for the PQC and Crypto Refresh code

[TJ-91]

I've been building the experimental Crypto Refresh and PQC code on Windows (Visual Studio 2022) and got a few errors.

• On Windows, the compiler complains about a deleted copy constructor so I provide one (via the already-implemented copy-assign constructor).
• I also fixed a minor variable-length array issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6a15c33) 76.89% compared to head (40b53ab) 76.88%.

❗ Current head 40b53ab differs from pull request most recent head 96a1c63. Consider uploading reports for the commit 96a1c63 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2135      +/-   ##
==========================================
- Coverage   76.89%   76.88%   -0.01%     
==========================================
  Files         193      193              
  Lines       37029    37030       +1     
==========================================
- Hits        28472    28471       -1     
- Misses       8557     8559       +2     

see 3 files with indirect coverage changes

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[maxirmx]

@ni4 @ronaldtse
vcpkg installs botan-3 by default now and windows workflows are configured to use botan-2

There is a piece of code in rnp/src/lib/CMakeLists.txt that shall handle this case

if (CRYPTO_BACKEND_BOTAN3)
  find_package(Botan 3.0.0 REQUIRED)
elseif (CRYPTO_BACKEND_BOTAN)
  find_package(Botan 2.14.0 REQUIRED)
  if(BOTAN_VERSION VERSION_GREATER_EQUAL 3.0.0)
    set(CRYPTO_BACKEND_BOTAN3 1)
  endif()
endif()

but build script fails earlier.

[TJ-91]

This is now also addressed in #2142 but I will leave this PR open since it contains an open issue raised by @maxirmx

@maxirmx: Feel free to close this and make a separate issue

[maxirmx]

Windows issue with FindBotan has been fixed:
#2138