fix(translation): wire v2 tests into CI and clear the code-quality gate

The new tests/test_litellm/translation suite was in no CI shard, so it never
ran and codecov reported 0% patch coverage; add it to the misc unit-test
workflow and the Makefile group so it runs and reports

Allowlist the boundary JSON walkers freeze and thaw in recursive_detector, the
same treatment every other cycle-free JSON/schema walker gets (bounded by input
nesting depth, no cycles possible in JSON)

Drop the unused engine/http.py I/O port; it had no caller in a request-only
slice, so it was dead code with zero coverage. The injected port returns with
the response and stream increment that actually performs I/O

Add failures-as-values tests covering the parser's error branches (malformed
roles, content parts, images, tools, tool_calls, tool_choice) and four more
differential parity cases: system as array, stop as string,
max_completion_tokens, and a tool without a description

tests/code_coverage_tests/recursive_detector.py

@@ -50,6 +50,8 @@ IGNORE_FUNCTIONS = [
     "_resolve",  # OCI: $ref resolver bounded by `resolving_stack` cycle guard.
     "resolve_oci_schema_anyof",  # OCI: bounded by JSON-schema tree depth (no cycles possible in well-formed input).
     "sanitize_oci_schema",  # OCI: bounded by JSON-schema tree depth.
+    "freeze",  # translation/boundary: plain JSON -> frozen IR walker, bounded by input nesting depth (no cycles possible in JSON).
+    "thaw",  # translation/boundary: inverse of freeze, bounded by IR nesting depth (no cycles possible).
 ]