Fix OpenSSL library loading for MariaDB authentication plugins

[quinnj]

Summary

• Pre-load OpenSSL libraries with RTLD_GLOBAL to fix plugin loading on macOS/Linux
• Add OpenSSL_jll as explicit dependency

Problem

MariaDB authentication plugins (e.g., caching_sha2_password) depend on OpenSSL, but when MariaDB loads them via dlopen at runtime, the dynamic linker can't find OpenSSL because:

1. The plugin has @rpath/libssl.3.dylib as a dependency
2. The embedded rpath points to the MariaDB artifact root
3. OpenSSL is in a completely different artifact (Julia's installation directory)

Solution

Pre-load OpenSSL libraries with RTLD_GLOBAL when the API module initializes. This makes OpenSSL symbols globally available to subsequently loaded libraries, allowing the plugins to find them even though the @rpath can't resolve to the actual file location.

Test plan

• Verify package loads correctly
• Test connection to MySQL 8.0+ server using caching_sha2_password authentication (the default)

Fixes #232

---

@nakagami Could you please test this PR to verify it fixes the issue on your system? You can try it with:

using Pkg
Pkg.add(url="https://github.com/JuliaDatabases/MySQL.jl", rev="jq/fix-openssl-plugin-loading")

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.40%. Comparing base (d5c20f9) to head (c8b70a6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #233      +/-   ##
==========================================
+ Coverage   63.27%   63.40%   +0.13%     
==========================================
  Files           9       10       +1     
  Lines        1111     1115       +4     
==========================================
+ Hits          703      707       +4     
  Misses        408      408              

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