chore: adds DataSystem contract test support

[tanderson-ld]

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

SDK-1631

Describe the solution you've provided

Ports most of the dotnet logic for the TestService.java. Also adds payload filter query param handling to the FDv2 builders/sources so those filter tests pass.

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Note

Introduces FDv2 payload filtering and data system wiring, plus contract test harness tweaks.

• Adds payloadFilter support end-to-end: new setters on FDv2*Initializer/Synchronizer builders, DataSystemComponents plumbs it through, and DefaultFDv2Requestor now appends a filter= query param (with tests); SdkClientEntity consumes dataSystem.payloadFilter and configures FDv2 polling/streaming initializers/synchronizers accordingly
• Expands contract test representations with dataSystem config types (initializers, synchronizers, store stubs, cache modes) and adds handling in SdkClientEntity (persistent store code left TODO)
• Makefile: configurable TEST_SERVICE_PORT, introduce suppression files, update harness runs (v2 with -skip-from, add v3.0.0-alpha.1 run), and add contract-tests/test-suppressions-fdv2.txt

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