feat(node-sdk): Improve feature overrides

[roncohen]

• include a testing section
• rewrote many tests for Client because it was difficult to work with because of mocking and many asserts.

[Copilot]

Pull Request Overview

This PR enhances the Node SDK’s feature override functionality by allowing direct object-based overrides, adding a clearFeatureOverrides method, refactoring tests for better clarity with flattenJSON, and documenting testing patterns.

• Extend featureOverrides setter to accept plain objects and introduce clearFeatureOverrides.
• Refactor client tests to use flattenJSON and streamlined event filtering.
• Add a “Testing” section in the README with usage examples.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/node-sdk/src/client.ts	Added object-based overrides support, clearFeatureOverrides, and adjusted mapping
packages/node-sdk/test/client.test.ts	Imported flattenJSON and simplified HTTP event assertions
packages/node-sdk/example/app.test.ts	Updated example tests to use object override syntax
packages/node-sdk/README.md	Added “Testing” section with feature override examples

Comments suppressed due to low confidence (1)

packages/node-sdk/README.md:430

• The example uses bucket.setFeatureOverride but the setter is named featureOverrides. It should read bucket.featureOverrides = { ... }.

    bucket.setFeatureOverride = {