fix: bundle Windows OpenSSL runtime libraries

[vik-borisov]

Summary

• Export OpenSSL runtime DLLs with the Windows libgit2 artifact.
• Bundle versioned libcrypto*.dll and libssl*.dll in Windows Flutter apps.
• Load bundled Windows OpenSSL DLLs before libssh2.dll in the package-root fallback loader.
• Prepare release metadata for 1.11.4.

Validation

• flutter test test\windows_packaging_test.dart
• git diff --check

Notes

Local dart pub publish --dry-run in a source checkout still cannot complete because lib/src/bindings.dart is produced by the CI generate_bindings artifact and is downloaded in the publish_package job before publishing.