Refactor: eliminate redundant JSON unmarshals in produce-policy validators; use slices.Contains in env_sources

[Copilot]

Two minor simplifications to align recently added code with existing codebase patterns.

Changes

• event_gateway_produce_policy.go — UnmarshalJSON was calling json.Unmarshal 4× (meta struct + 2 validators + SDK union type). Parse data into map[string]any once after the meta extraction and pass it to both validators, matching the pattern in event_gateway_consume_policy.go. Also eliminates 3 intermediate string variables (modifyHeadersType, schemaValidationType, encryptType) in favor of direct validTypes slice indexing.

  // Before: each validator parsed data independently
  func validateProducePolicyTypeField(data []byte) error {
      var raw map[string]any
      if err := json.Unmarshal(data, &raw); err != nil { ... }
      ...
  }
  
  // After: parse once, pass map
  var raw map[string]any
  if err := json.Unmarshal(data, &raw); err != nil { return err }
  if err := validateProducePolicyTypeField(raw); err != nil { return err }
  if err := validateProducePolicyConfigField(raw); err != nil { return err }

• env_sources.go — Replace 3-line manual loop in parseStructuredFieldTag with slices.Contains(parts[1:], "inline"), consistent with Go 1.26 idioms used throughout the codebase.

[Copilot]

Pull request overview

This PR streamlines declarative parsing by reducing redundant JSON unmarshalling in the Event Gateway produce policy resource and simplifying struct-tag parsing logic in the loader using standard library slice helpers.

Changes:

• Unmarshal produce policy JSON into a map[string]any once and reuse it across validators (aligning with the existing consume policy pattern).
• Simplify produce policy type validation by centralizing allowed types in a single slice and using slices.Contains.
• Replace a manual "inline" tag scan loop with slices.Contains in structured tag parsing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/declarative/resources/event_gateway_produce_policy.go	Parse JSON once for validators and simplify allowed-type handling in produce policy unmarshalling/validation.
internal/declarative/loader/env_sources.go	Use slices.Contains to detect "inline" in structured field tags, reducing boilerplate.

[rspurgeon]

@harshadixit12 please review