Mockingoose v3: TypeScript rewrite, Mongoose 9, Vitest

[alonronin]

Summary

 Major rewrite of mockingoose for modern Mongoose and TypeScript ecosystems.

 - **TypeScript rewrite** — Full rewrite from JavaScript to TypeScript with dual ESM/CJS output (`tsdown`), proper `exports` map,
 and generated `.d.ts` files
 - **Mongoose 9 support** — Peer dependency bumped to `^9.1.6`; removed deprecated ops (`count`, `update`, `remove`,
 `findOneAndRemove`); all tests use async/await
 - **New operations** — Added `replaceOne`, `bulkWrite`, `bulkSave`, and `cursor` support
 - **Jest → Vitest** — Test runner migrated to Vitest with `globals: true`; runtime auto-detects Jest or Vitest for mock function
 creation
 - **CI modernized** — CircleCI → GitHub Actions (Node 20 + 22); added release-please for automated npm publishing
 - **Node ≥20** — Dropped Node 18 (EOL April 2025); required by Vitest 4 / Vite 7

 ## Breaking Changes
 - Minimum Node.js version: **20** (was 6.4)
 - Minimum Mongoose version: **9.x** (was 4.9)
 - Removed operations: `count()`, `update()`, `remove()`, `findOneAndRemove()`
 - Build output moved from `lib/` to `dist/` (new `exports` map — transparent to consumers)

 ## Test plan
 - [x] `bun run test` — 95 tests passing
 - [ ] `bun run build` — dual ESM/CJS output
 - [ ] `bun run typecheck` — no type errors
 - [ ] CI passes on Node 20 + 22