feat(build): add CommonJS build output and package entrypoints (#156)

[vihaan-vijay]

Summary

Fixes #156

This PR adds dual-module distribution support by adding CommonJS (CJS) package entrypoints and conditional exports alongside the existing ES Modules (ESM) build outputs across @spotify-confidence/sdk and related workspace packages.

Problem

Projects relying on CommonJS require() syntax or TypeScript tooling running with default CommonJS settings (e.g. ts-node) encountered ERR_PACKAGE_PATH_NOT_EXPORTED errors because:

• The package.json manifest lacked top-level "main", "module", and "types" properties.
• The "exports" configuration map in package.json did not define a "require" conditional export pointing to CommonJS build artifacts.

Changes Made

1. Yarn Constraints & Package Manifests (yarn.config.cjs & package.json):
   • Updated yarn.config.cjs to enforce "main", "module", "types", and "exports" invariants across workspace packages.
   • Configured "main": "dist/index.cjs", "module": "dist/index.mjs", and "types": "dist/index.d.ts".
   • Added "require": "./dist/index.cjs" to the "exports" condition map.
2. Cross-Platform Build Normalization (rollup.base.mjs):
   • Normalized Windows backslashes (\) to forward slashes (/) in normalizePath so Rollup bundling executes cleanly across Windows and POSIX environments.
3. CJS Integration Test (packages/sdk/src/cjs.test.ts):
   • Added a unit test ensuring @spotify-confidence/sdk CommonJS artifacts can be required and cleanly expose exported interfaces (Confidence, Value, etc.).

Verification

• Unit Tests: Ran yarn test — all 16 test suites (175 tests) passed cleanly.
• Node.js CJS Resolution: Verified require('@spotify-confidence/sdk') in Node.js runtime without errors.
• Node.js ESM Resolution: Verified import { Confidence } from '@spotify-confidence/sdk' in ESM runtime without errors.
• Yarn Constraints: Verified yarn constraints passes without constraint errors.