feat: adding isomorphic provider to bridge client and server

[joker23]

SDK-1946

• modify the server-only example to demonstrate how to use the isomorphic provider
• modify the bundling so client and server can still bundle correcly with isomorphic components
• refactor the client side NOOP client to be able to execute well during SSR

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Note

Medium Risk
Introduces new RSC/client provider components and adjusts server bundling to depend on the client entrypoint, which could affect SSR/hydration behavior and packaging if misconfigured. Behavior change in createNoopClient initialization state may impact consumers relying on that signal during SSR tests.

Overview
Adds an isomorphic bootstrap flow for React Server Components: new server LDIsomorphicProvider evaluates session.allFlagsState({ clientSideOnly: true }), serializes it via toJSON(), and renders a new 'use client' LDIsomorphicClientProvider that uses those values as client bootstrap.

LDIsomorphicClientProvider selects SSR vs browser behavior: on the server it creates a noop client (via createNoopClient) and wraps children with createLDReactProviderWithClient; in the browser it initializes the real provider via createLDReactProvider, merging passed options with bootstrap.

Updates packaging/exports to surface the new APIs (client/index.ts, server/index.ts) and tweaks build config so the server bundle treats @launchdarkly/react-sdk as external. Refines createNoopClient to always report getInitializationState() as 'initializing', adds unit tests for the new providers, and updates the server-only example/docs to demonstrate bootstrapped client + server rendering (including new LAUNCHDARKLY_CLIENT_SIDE_ID requirement and e2e expectation changes).

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25661 bytes
Compressed size limit: 29000
Uncompressed size: 126143 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179253 bytes
Compressed size limit: 200000
Uncompressed size: 828804 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31446 bytes
Compressed size limit: 34000
Uncompressed size: 111621 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 37015 bytes
Compressed size limit: 38000
Uncompressed size: 202741 bytes

[joker23]

Thoughts on this?

[joker23]

In general, I think this example name should be changed to something like react-server-example. Might want to do this in a separate change since that could add a lot of distracting changes.

[joker23]

@cursor review

[joker23]

The typing here is to be consistent with browser sdk

[joker23]

@cursor review