Migrate to turborepo

[julianschiller]

Closes #

Migrates the monorepo from Lerna to Turborepo (task running with caching) and Changesets (versioning & publishing). Main reason: Lerna pulls in nx along with a large transitive dependency tree that we want to get rid of. Nothing changes for the published packages — only the internal build and release tooling.

Changelog

New

• turbo.json with cached build/test/lint tasks and topological ordering (^build)
• Changesets setup (.changeset/config.json) in fixed mode — all packages are versioned together, same as before
• Per-package lint script, run via turbo run lint
• A .eslintignore in each package that has generated files, so those files aren't linted

Changed

• Root scripts switched from Lerna to Turbo: build, test, lint:check
• update:lock / update:registry now use native npm workspaces instead of lerna exec/lerna run
• release.yml uses Changesets instead of lerna publish — the manual workflow_dispatch (patch/minor/major) is kept
• continuous.yml additionally caches .turbo

Removed

• lerna and nx from devDependencies (including the transitive @nrwl/* tree)
• lerna.json

[hirsch88]

well done. thxs