Improvement: proxy-core - Refactor service_resolver

[arvindr19]

Description

Currently, fucntions are implemented across multiple ServiceResolver impl blocks in different files:

• resolve.rs: direct CDA manager calls (lookup_diagcomms_by_request_prefix, get_request_parameter_metadata)
• metadata.rs: query methods (get_service_parameter_metadata, get_response_parameter_metadata, get_enriched_response_metadata_with_source)
• response.rs: calls to enriched metadata methods

making harder to read, harder to maintain, test, and extend.

Additional Context

Related PR: #11