bump to go vips 2.19

[n0vad3v]

• Upgrade govips from v2.18.0 to v2.19.0.
• Stop image conversion when preprocessing fails.
• Remove the redundant WebP encoding call after the retry loop.
• Add a regression test to ensure oversized images do not produce output.
• Bump version to 0.16.1

[github-actions]

Report Summary

┌──────────────────────────────────────────────┬──────────┬─────────────────┬─────────┐
│                    Target                    │   Type   │ Vulnerabilities │ Secrets │
├──────────────────────────────────────────────┼──────────┼─────────────────┼─────────┤
│ ghcr.io/webp-sh/webp_server_go (debian 13.7) │  debian  │        0        │    -    │
├──────────────────────────────────────────────┼──────────┼─────────────────┼─────────┤
│ usr/bin/webp-server                          │ gobinary │        0        │    -    │
└──────────────────────────────────────────────┴──────────┴─────────────────┴─────────┘
Legend:
- '-': Not scanned
- '0': Clean (no security findings detected)