refactor: update client based on API spec changes

[tharropoulos]

Change Summary

• Analytics rule types: Consolidated AnalyticsRuleCreateType into AnalyticsRuleType; renamed constants (e.g., AnalyticsRuleTypeCounter → Counter)
• Schema consolidation: Removed CurationSetRetrieveSchema and SynonymSetRetrieveSchema; use CurationSetSchema and SynonymSetSchema directly
• Synonym items: Split into SynonymItemSchema (with id) and SynonymItemUpsertSchema (without id) for upsert operations
• Field additions:
  • Added async_reference to Field schema
  • Added top-level fields to MultiSearchResult (found, out_of, search_time_ms, page, search_cutoff, facet_counts, grouped_hits, metadata, request_params, union_request_params)
• OpenAPI spec: Formatting cleanup (quotes, indentation, anyOf → oneOf, description formatting)
• Tests: Updated to use new enum names; added test for multi-search with top-level fields
• Dependencies: Updated Go to 1.24.0 and bumped golang.org/x/* packages

PR Checklist

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