test: integration tests for Rego V1 dual-parse pipeline (Phase 1)

[dakshhhhh16]

Part of #5262
Phase -1 Leftover part (Marking the end of phase 1)

Problem

The Phase 1 dual-parse infrastructure (DB migration, DetectRegoVersion(), service wiring, evaluator option, feature flag) was implemented but lacked integration tests verifying the full pipeline end-to-end:

• No test verified that RegoVersion is correctly detected and passed to DB on CreateRuleType / UpdateRuleType
• No test verified that V1 Rego policies evaluate correctly when WithRegoVersion(ast.RegoV1) is used
• No edge-case tests for version detection (V0 function syntax, every keyword, comprehension-heavy policies, syntax errors)

Changes

pkg/ruletypes/service_test.go

• Custom gomock.Matcher (regoVersionMatcher) that inspects the RegoVersion field in CreateRuleTypeParams / UpdateRuleTypeParams
• withRegoEval(def) test helper to build rule types with Rego eval definitions
• 5 new test scenarios:
  • CreateRuleType with V0 Rego → DB gets rego_version = "v0"
  • CreateRuleType with V1 Rego → DB gets rego_version = "v1"
  • CreateRuleType without Rego eval → DB gets rego_version = "v0"
  • UpdateRuleType with V0 Rego → DB gets rego_version = "v0"
  • UpdateRuleType with V1 Rego → DB gets rego_version = "v1"

internal/engine/eval/eval_test.go

• 3 table-driven tests verifying WithRegoVersion option works through NewRuleEvaluator:
  • V1 deny-by-default policy evaluates with ast.RegoV1
  • V1 constraints policy evaluates with ast.RegoV1
  • V0 policy works with explicit ast.RegoV0 option (regression)
• Dedicated test: V1 policy returns success when input matches

internal/engine/eval/rego/version_test.go

• 5 new edge-case detection tests:
  • V0 function syntax (format_message(...) = msg { ... })
  • V1 function syntax (format_message(...) := msg if { ... })
  • V0 partial set with comprehensions
  • V1 every keyword
  • Syntax error falls back to V0

[dakshhhhh16]

@evankanderson
Just waiting for the first part pr to get merged first, the pr for this is ready and will be pushed after the merge of #6317
and this marks the end of phase 1