feat: Update contract tests to support multiple synchronizers and initializers

[devin-ai-integration]

BEGIN_COMMIT_OVERRIDE
chore: Update contract tests to support multiple synchronizers and initializers
END_COMMIT_OVERRIDE

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

Related to sdk-test-harness commit: launchdarkly/sdk-test-harness@01a245c

Describe the solution you've provided

Updates the contract test implementation to match the sdk-test-harness changes that add support for multiple synchronizers (more than 2) for testing fallback scenarios.

Contract test model changes:

• Changed SdkConfigDataSystemParams.Synchronizers from SdkConfigSynchronizersParams (with Primary/Secondary properties) to SdkConfigDataSynchronizerParams[] (array)
• Removed the SdkConfigSynchronizersParams class
• Renamed SdkConfigSynchronizerParams to SdkConfigDataSynchronizerParams for consistency
• Updated SdkClientEntity.BuildSdkConfig to iterate over the synchronizers array

CI config change:

• Pinned FDv2 contract tests to use the v3.0.0-alpha.3 tag of sdk-test-harness instead of the feat/fdv2 branch

Human review checklist

• Verify v3.0.0-alpha.3 tag exists in sdk-test-harness and is compatible with the array-based synchronizer format used here
• Verify the FDv1 fallback synchronizer selection logic is correct — it now picks the first polling synchronizer found in the array, or falls back to the first synchronizer if none have polling configured
• Confirm the JSON serialization matches what the test harness sends (property names are auto-camelCased)

Describe alternatives you've considered

Could have kept backward compatibility by supporting both the old Primary/Secondary structure and the new array format, but this would add unnecessary complexity since the test harness has moved to the array-based approach.

Additional context

• Link to Devin run: https://app.devin.ai/sessions/5d71cc37cb45475088773207ef7fd987
• Requested by: rlamb@launchdarkly.com

This is a contract test and CI config change only — no changes to the SDK itself.

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Note

Medium Risk
Moderate risk due to a breaking change in the contract-test config model (Synchronizers shape) and updated fallback-selection behavior that could alter FDv2/FDv1 test execution, though it is confined to test/CI code.

Overview
Updates the contract test data-system configuration model to support multiple synchronizers by changing SdkConfigDataSystemParams.Synchronizers from a Primary/Secondary object to an array of SdkConfigDataSynchronizerParams (and removing/renaming the old types).

Adjusts SdkClientEntity.BuildSdkConfig to build all provided synchronizers, and changes FDv1 fallback selection to pick the first polling synchronizer found (otherwise the first synchronizer). CI’s FDv2 contract test action is also updated to run sdk-test-harness from the pinned v3.0.0-alpha.3 tag instead of the feat/fdv2 branch.

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[devin-ai-integration]

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