chore: upgrade ESLint and TypeScript tooling

[rainerhahnekamp]

Upgrade the root development tooling:

• eslint to 10.3.0
• typescript to 6.0.3
• typescript-eslint and @typescript-eslint/rule-tester to 8.59.3
• eslint-config-prettier to 10.1.8
• eslint-plugin-prettier to 5.5.5
• eslint-plugin-unused-imports to 4.4.1
• @types/eslint to 9.6.1
• @types/estree to 1.0.9
• @types/node to 24.12.4

Refresh yarn.lock for the updated dependency graph.

Compatibility changes:

• Allow ESLint 10 in @softarc/eslint-plugin-sheriff peer dependencies.
• Add TypeScript 6 deprecation acknowledgement in tsconfig.base.json.
• Replace Array.prototype.at() usage in library code so the current es2017 lib still type-checks.
• Update ESLint rule context access to use current ESLint 10 properties instead of removed/deprecated methods.

Verification performed:

• yarn lint:all passed.
• ./node_modules/.bin/tsc -p packages/core/tsconfig.lib.json --noEmit passed.
• ./node_modules/.bin/tsc -p packages/eslint-plugin/tsconfig.lib.json --noEmit passed.
• yarn vitest --run passed: 43 files, 347 passed, 2 skipped.

Known remaining environment/test notes:

• yarn test:ci still fails in the full integration specs because built package resolution cannot find @softarc/sheriff-core.
• yarn build:all could not complete in the Codex sandbox because Nx project graph/daemon handling failed around Unix socket/plugin-worker startup.
• Direct TypeScript package checks passed, so the dependency migration itself is type-safe in this workspace.

Session context for resuming:

This was done after checking current npm registry metadata for ESLint, TypeScript, and typescript-eslint. The compatible path identified was ESLint 10.3.0, TypeScript 6.0.3, and typescript-eslint 8.59.3, whose peer ranges include ESLint 10 and TypeScript >=4.8.4 <6.1.0.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud