fix: isolate walk state from Object prototype

[LaplaceYoung]

Summary

• Initialize walk()'s visited-name table with a null prototype so inherited Object.prototype properties cannot interfere with tracking.
• Add source-level and issue-level regression coverage for sinon.stub() when Object.prototype has an inherited non-writable property.
• Make the local build, Node test, and lint commands run on Windows by invoking the local Rollup CLI and using cross-platform globs.

Verification

• npm run test-node (1534 passing, 12 pending)
• npm run lint
• npx prettier --check build.cjs rollup.config.mjs package.json src/sinon/util/core/walk.js test/src/util/core/walk-test.js test/issues/issues-test.js
• Source reproduction script now prints stub created

Fixes #2702

[fatso83]

Thank you!