fix: avoid mutating ssl connection options

[puneetdixit200]

Fixes #2380.

This copies SSL option objects before applying the default rejectUnauthorized value. The connection config still defaults rejectUnauthorized to true, but the caller-provided ssl object and shared SSL profile objects are left unchanged.

Validation:

• FILTER=unit/test-ConnectionConfig npm_config_cache=/tmp/mysql-2380-npm-cache npm test
• npm_config_cache=/tmp/mysql-2380-npm-cache npm run lint
• Reproduction check: mysql.createConnection({ ssl: {} }) leaves the original config as { "ssl": {} } while connection.config.ssl.rejectUnauthorized is true
• Broader FILTER=unit npm test was attempted on Node 24 and Node 18; existing SSL fake-server tests fail locally because modern OpenSSL rejects the repo test certs (ee key too small on Node 24, expired certificate on Node 18), while the focused config tests pass.