feat(types): Adding null int and null int 32

[Jacobbrewer1]

Describe your changes

This pull request includes several changes to improve the handling of nullable integer types and to streamline the build process using Mage. The most important changes are grouped by their themes below:

Enhancements to nullable integer types:

• Added NullInt type with support for JSON marshaling, SQL scanning, and Redis argument interfaces in usql/types.go.
• Added NullInt32 type with similar support for JSON marshaling, SQL scanning, and Redis argument interfaces in usql/types.go.
• Updated getType function to return usql.NullInt for nullable int columns and usql.NullInt32 for nullable mediumint columns in pkg/generation/template_helpers.go. [1] [2]

Streamlining the build process:

• Replaced inline Mage commands with magefile/mage-action GitHub action in .github/workflows/create-release.yml to improve the build process.