fix: export Schema and additional schemas

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fixes #121

Breaking Changes

No

Additional Info

No

[sethamus]

I believe this change is likely why ESLint CI started to fail.

Run npm run lint:types > eslint-webpack-plugin@[5](https://github.com/eslint/eslint/actions/runs/14600143793/job/40956026705?pr=19648#step:7:6).0.1 lint:types > tsc --pretty --noEmit node_modules/webpack/types.d.ts:9[6](https://github.com/eslint/eslint/actions/runs/14600143793/job/40956026705?pr=19648#step:7:7):2 - error TS2305: Module '"schema-utils/declarations/validate"' has no exported member 'Extend'. 96 Extend, ~~~~~~ Found 1 error in node_modules/webpack/types.d.ts:[9](https://github.com/eslint/eslint/actions/runs/14600143793/job/40956026705?pr=19648#step:7:10)6 Error: Process completed with exit code 2. 

[alexander-akait]

@sethamus Because some types was internally renamed, you should use a new name - ExtendedSchema

[alexander-akait]

But looks like more developers use it, fix here - #198