[AFCMS]

Replace the TypeScript build with tsdown to generate JavaScript, declarations, package exports and the CLI executable.

• Upgrade to TypeScript 7 and add a separate typecheck step.
• Replace ESLint and Prettier with Oxlint and Oxfmt.
• Remove unused dependencies found with knip: @publint/pack, package-manager-detector, semver, @types/picomatch and @types/semver.
• Drop Node 20 support since it has reached EOL. Declare Node 22+ as the minimum supported runtime and test Node 22, 24 and 26 in CI.
• Enable tsdown’s publint and attw checks to validate package exports and TypeScript declarations.
• Preserve the e18e-cli command name.

I have successfully tested the CLI on my own projects, plus the API with a Codex generated comparaison test suite (latest master + patch).