docs: add provider lifecycle guidance

[zhouzhou626]

Summary

• Document provider readiness during Evaluation API provider registration, including links to PROVIDER_READY and PROVIDER_ERROR event guidance.
• Add an Evaluation API shutdown section with TypeScript, Java, and Python examples.
• Add provider lifecycle guidance with initialization/shutdown examples for TypeScript and Java.
• Update the Java Evaluation API import to the current dev.openfeature.sdk package used by the Java SDK docs.

Closes #119.

Testing

• corepack yarn install --immutable
• git diff --check
• corepack yarn markdownlint-cli2 docs/reference/concepts/01-evaluation-api.mdx docs/reference/concepts/02-provider.mdx --no-globs
• corepack yarn prettier --check docs/reference/concepts/01-evaluation-api.mdx docs/reference/concepts/02-provider.mdx

Additional checks attempted:

• git submodule update --init --recursive
• corepack yarn build reaches Docusaurus/Webpack but is blocked in this Windows workspace by an existing parent-directory JSON parse issue: D:\CodexWork\package.json contains a BOM and PostCSS reports Unexpected token '?' while loading CSS modules.
• corepack yarn typecheck is blocked by existing repository issues unrelated to this docs change, including missing ./OpenFeatureTechnologiesPage, missing static image modules, and an existing SearchClient type incompatibility in src/pages/ecosystem.tsx.

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[gemini-code-assist]

Code Review

This pull request updates the documentation for the Evaluation API and Provider concepts, including a correction to Java package imports and the addition of sections regarding provider initialization and API shutdown. Feedback was provided to ensure the Java code example for the provider lifecycle matches the SDK's interface signature by adding a 'throws Exception' clause to the shutdown method.

[gemini-code-assist]

In the OpenFeature Java SDK, the shutdown method in the FeatureProvider interface is defined with a throws Exception clause. While it is technically valid in Java to override a method and omit the throws clause if the implementation doesn't throw checked exceptions, it is better for documentation examples to match the interface signature for consistency with the initialize method shown above.

    @Override
    public void shutdown() throws Exception {