chore: Declare the hook-environment-id contract test capability

[kinyoklion]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Depends on launchdarkly/sdk-test-harness#410, which adds the hook-environment-id capability and a test asserting evaluationSeriesContext.environmentId.

Describe the solution you've provided

Only the capability declaration was needed: TestHook posts the EvaluationSeriesContext itself, and the callback serializer's camel-case policy already renders EnvironmentId as environmentId.

Verified with a local build of the harness branch against the server contract test service (net8.0): hooks/evaluation/provides the environment ID passes with no other change.

Describe alternatives you've considered

None; no behavior change is needed.

Additional context

The capability only takes effect once the harness change is released; until then the harness ignores it. The client SDK is untouched.

Link to Devin session: https://app.devin.ai/sessions/bfe54128e2804a96bb100e6120e9a3ef
Requested by: @kinyoklion

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Note

Overview
Registers hook-environment-id on the server contract test service’s capability list so the SDK test harness can run the evaluation-hook test that checks evaluationSeriesContext.environmentId.

No SDK or TestHook changes: the harness only runs that scenario when the capability is advertised, and existing serialization already exposes EnvironmentId as environmentId.

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[devin-ai-integration]

@cursor review