Listen, Notify statements support for Postgresql

[manhrev]

Summary

• Added psql.Listen() and psql.Notify() query builders for PostgreSQL's asynchronous notification system, with query mods in lm and nm packages
• Extended bobgen-psql parser to recognize and generate query mods for LISTEN and NOTIFY statements
• Extended bobgen-psql and bobgen-sqlite parsers to support top-level VALUES queries; MySQL support is partial (the parser don't support VALUES as subquery for now - TODO later)
• Added unit tests for LISTEN and NOTIFY
• Address Support for PostgreSQL's listen/notify #479

Notes

• LISTEN requires a persistent connection and only registers the channel subscription — receiving actual notifications must be implemented using your specific database driver (e.g. pgx's WaitForNotification).