Migrate to @playcanvas/eslint-config v3 (/typescript)

[kpal81xd]

Migrates this repo to @playcanvas/eslint-config v3, adopting the /typescript subpath tier. Part of the rollout in playcanvas/eslint-config#48.

Changes

• Subpath migration: import playcanvasConfig from '@playcanvas/eslint-config' → import typescriptConfig from '@playcanvas/eslint-config/typescript'. The /typescript tier provides the typescript-eslint parser + plugin (for **/*.{js,mjs,ts}, globals.node) and the import-x resolver out of the box.
• Removed redundant wiring: dropped the manual @typescript-eslint/parser + @typescript-eslint/eslint-plugin imports and their parser/plugin config blocks, the manual import/resolver node-settings block (now supplied by the tier), and the now-defunct jsdoc/* rule overrides (the /typescript tier has no jsdoc plugin).
• Namespace: renamed import/no-unresolved → import-x/no-unresolved (v3 registers eslint-plugin-import-x natively).
• Kept the repo-specific **/*.ts extra globals (browser + mocha + node), no-use-before-define: off, and the test-file no-unused-expressions: off block.
• Dependency bump: pinned @playcanvas/eslint-config to 3.0.0-beta.6 (carries the import-x resolver fix) and removed @typescript-eslint/eslint-plugin + @typescript-eslint/parser from devDependencies (only referenced by the old config; the tier now provides them). Regenerated package-lock.json.

Auto-fixed (lint:fix)

3 source files auto-fixed (src/history.ts, src/observer-history.ts, src/observer.ts): import-x/consistent-type-specifier-style (value→type imports), redundant default-value type annotations, and stale eslint-disable directives.

Follow-up lint pass

• Added Observer<T> top-level typing for get, set, patch, and json, plus ObserverList<T> and ObserverHistory<T> coverage in test/types.ts.
• Replaced explicit dynamic any annotations with a shared Value type.
• Fixed direct hasOwnProperty, arguments, and simple indexed-loop lint errors.
• Added the TS-namespaced Chai assertion override for test files.

Verification

• npm run lint
• npm run type:check
• npm run build
• npm test