Add caching for API keys in ProviderService

[ASCE-D]

Summary by CodeRabbit

• Refactor

  • Improved API key handling: adds memoized caching of provider credentials to reduce repeated lookups and improve reliability.
  • Introduces transparent fallbacks to provider-specific configuration when primary secrets are unavailable, reducing failures and latency.

• Style

  • Reformatted tool initialization code for clearer readability and easier maintenance.

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