chore: Remove LDConfig requirement from top level DS function helpers

[keelerm84]

Note

Refactors data system builders to be config-aware and updates FDv2/client integration and tests accordingly.

• Data system config API:
  • Change Builder type to Callable[[Config], T] in ldclient/config.py and impl/datasystem/config.py.
  • Convert default(), streaming(), polling(), daemon(), persistent_store() to no-arg helpers that return builders which accept Config.
  • Internal polling/streaming builder factories now return functions (config) -> DataSource.
• FDv2:
  • Update constructor to FDv2(config: Config, data_system_config: DataSystemConfig) and derive offline state from config.offline.
  • Use data_system_config for initializers/synchronizers/store; pass config into initializer/synchronizer builders.
  • Minor logging cleanup to parameterized logging.
• Client:
  • Instantiate FDv2 with FDv2(self._config, datasystem_config).
• TestDataV2:
  • build_initializer/build_synchronizer now accept a Config arg (unused) to match new Builder signature.
• Tests:
  • Update all tests to new signatures and helper APIs; add Config(sdk_key="dummy") where needed.
  • Minor formatting adjustments in test stubs.

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