feat!: replace rsyncwrapper with direct child_process.spawn

Remove the outdated rsyncwrapper dependency (unmaintained, uses
deprecated util._extend) and replace with a built-in buildRsyncCommand()
+ spawn implementation. Zero runtime dependencies.

BREAKING CHANGE: rsyncwrapper dependency removed, rsync command is now
constructed and executed directly via child_process.spawn.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -29,9 +29,6 @@
     "url": "https://github.com/easingthemes/ssh-deploy/issues"
   },
   "homepage": "https://github.com/easingthemes/ssh-deploy#readme",
-  "dependencies": {
-    "rsyncwrapper": "^3.0.1"
-  },
   "devDependencies": {
     "@vercel/ncc": "^0.36.0",
     "eslint": "^8.30.0",