apollo_node_config: promote normalize_pointer_groups to shared config_utils test helper

[nimrod-starkware]

Move the pointer-group normalization helper from config_test.rs to config_utils.rs as a pub
#[cfg(any(feature = "testing", test))] fn so cross-crate tests can reuse it. Pure refactor:
config_test remains the sole caller here. Adds starknet_api to [dependencies] since config_utils is
a non-test source file.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[nimrod-starkware]

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• apollo_network,apollo_config: use native serde for bootstrap_peer_multiaddr #14848
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• deployment: move all jsonnet files together #14806
• deployment,scripts: remove dead configList config key #14804
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• apollo_deployments,apollo_integration_tests: source harness component configs from jsonnet #14687
• deployment: drop redundant YAML sequencerConfig; source port-uniqueness from jsonnet #14659
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• apollo_config,apollo_node_config,apollo_config_manager: rework get_config_presentation off dump() #14653
• apollo_node_config,apollo_node: delete CONFIG_POINTERS data and pointer-remap from secrets bin #14652
• apollo_node_config,apollo_config_manager,apollo_integration_tests: retire preset config-generation path #14651
• apollo_node_config: promote normalize_pointer_groups to shared config_utils test helper #14731 👈 (View in Graphite)
• apollo_node_config,apollo_deployments: assert cross-component equality for formerly-pointer-resolved fields #14650
• apollo_deployments: delete base app_configs and the preset-parity test machinery #14649
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• apollo_deployments: retire dead preset/replacer generation machinery #14647
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• apollo_config,apollo_node_config: make config fields with custom deserializers serialize symmetrically #14630
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• deployment: add mainnet native config override layer #14628
• deployment: add sepolia-alpha native config override layer #14627
• deployment: add sepolia-integration native config override (chain_params + replacers) #14674 : 1 other dependent PR (#14626 )
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• apollo_deployments: assemble and deserialize node config from jsonnet #14487
• apollo_deployments: assemble full node config via build.libsonnet #14486
• apollo_deployments: distributed layout jsonnet test #14485
• apollo_deployments: consolidated layout jsonnet test #14484
• apollo_deployments: test hybrid layout for infra config #14483
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• apollo_deployments: introduce jsonnet building blocks for infra config #14481
• apollo_deployments: jsonnet applicative config #14479
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