v1.31.3

Chore

• Limit maximum MIME parts parsed per message to 500
• Refactor regex usage for string cleaning and normalization
• Optimize envelope parsing by using a shared parser instance
• Optimize message summary construction by eliminating JSON round-trip
• Replace bytes.ToLower with containsFold for case-insensitive tag matching
• Replace inline regex for leading whitespace with a package-level variable
• Symlink sendmail to Mailpit in Docker image (#736)
• Update Go dependencies
• Update node dependencies
• Update GitHub Actions dependencies