[FSSDK-10843] prepare release 6.0.0

[raju-opti]

Summary

Test plan

Issues

• FSSDK-10843

[Copilot]

Pull Request Overview

This PR prepares the 6.0.0 release by updating version numbers and documentation in various files.

• Version updates in package.json, enums, and test files to reflect the new 6.0.0 release.
• Updates to migration and changelog documentation to describe the new modularized SDK architecture and related API changes.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
package.json	Updated version from "5.3.4" to "6.0.0".
lib/utils/enums/index.ts	Updated CLIENT_VERSION constant from "5.3.4" to "6.0.0".
lib/index.react_native.spec.ts	Updated test expectation to check for clientVersion "6.0.0".
lib/index.node.tests.js	Uncommented and updated tests to reflect the new version and use wrapConfigManager.
lib/index.browser.tests.js	Updated test expectation to check for clientVersion "6.0.0".
MIGRATION.md	Revised documentation to explain the new modularized SDK architecture.
CHANGELOG.md	Documented 6.0.0 release details including breaking changes and new APIs.

[coveralls]

coverage: 79.793% (+0.09%) from 79.7%
when pulling b433c92 on raju/prepare-6.0.0
into dd1375e on master.

[junaed-optimizely]

Finally! This is a big one.

Huge thanks for your expertise and dedication in driving this change — JS SDK is finally where it was meant to be!