chore: automate sqlite driver selection via build tags (#805)

[tejasva-vardhan]

Overview

This PR automates the SQLite driver selection for Maglev using Go build tags, directly addressing and resolving #805. It removes the friction for Windows developers who previously had to manually pass the -tags purego flag to build or run the project.

Changes Made

• Added driver_pure.go: Uses the //go:build windows && !cgo tag to automatically load modernc.org/sqlite on Windows machines without CGO.
• Added driver_cgo.go: Uses the //go:build !windows || cgo tag to preserve the high-performance mattn/go-sqlite3 driver for Linux/macOS and explicit CGO builds.
• Updated Dependencies: Ensured go.mod and go.sum correctly track both drivers.
• (Optional: If you included helpers.go) Refactoring: Replaced hardcoded "sqlite3"/"sqlite" strings with a cross-platform DriverName constant.

Verification

• Windows (No CGO): Verified that running go run ./cmd/api works out-of-the-box without GCC/MinGW toolchains.
• Linux/CGO Default: Verified that the build still defaults to the CGO driver for non-Windows environments to prevent any performance regressions.

Closes #805

[tejasva-vardhan]

@aaronbrethorst
i will update README in a follow-up after merge so this PR stays only about the driver change