Make codegen internal API private

[mizdra]

$ node
Welcome to Node.js v24.2.0.
Type ".help" for more information.
> require('@css-modules-kit/codegen')
Uncaught Error: Cannot find module '@css-modules-kit/codegen'
Require stack:
- <repl>
    at Module._resolveFilename (node:internal/modules/cjs/loader:1405:15)
    at defaultResolveImpl (node:internal/modules/cjs/loader:1061:19)
    at resolveForCJSWithHooks (node:internal/modules/cjs/loader:1066:22)
    at Module._load (node:internal/modules/cjs/loader:1215:37)
    at TracingChannel.traceSync (node:diagnostics_channel:322:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:235:24)
    at Module.require (node:internal/modules/cjs/loader:1491:12)
    at require (node:internal/modules/helpers:135:16) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [ '<repl>' ]
}
>

[changeset-bot]

🦋 Changeset detected

Latest commit: ab6ec41

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@css-modules-kit/codegen	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR