Embed Interface instead of Type

[winebarrel]

No description provided.

[Copilot]

Pull request overview

This PR refactors the generic database wrapper types (DB[T], Tx[T], Stmt[T]) to embed interfaces instead of concrete types from the database/sql package. This architectural improvement increases flexibility and follows best practices by programming to interfaces rather than implementations.

Changes:

• Changed DB[T], Tx[T], and Stmt[T] to embed interfaces (iface.DB, iface.Tx, iface.Stmt) instead of concrete types (*sql.DB, *sql.Tx, *sql.Stmt)
• Removed compile-time assertions from wrapper structs (they're no longer needed since the structs embed interfaces)
• Added a comprehensive example in cmd/main.go demonstrating type-safe database operations

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
db.go	Changed DB[T] to embed iface.DB interface instead of *sql.DB concrete type
tx.go	Changed Tx[T] to embed iface.Tx interface instead of *sql.Tx concrete type
stmt.go	Changed Stmt[T] to embed iface.Stmt interface instead of *sql.Stmt concrete type
cmd/main.go	Added new example demonstrating type-safe database operations with different database types

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