Retry target setup reads without recreating targets

[adamtheturtle]

A transient read failure during target_id setup restarted target creation, even after Vuforia had returned an ID. Retry processing polls and record reads against the existing target instead. Only an actual unsuccessful processing result triggers the existing bounded replacement behavior.

Attempt best-effort deletion if setup cannot return the target, while preserving the original error if cleanup also fails. The real adapter retains its cleanup of remaining targets before the next test.

Fixes #3767.

Validation:

• 12 deterministic regression cases cover 429, timeout and visibility recovery, exhausted reads, cleanup failure, and bounded replacement after failed processing.
• Full local suite excluding the real backend and Docker-build cases: 2,033 passed, 839 skipped.
• Pre-commit and pre-push hooks, including partition checks and all type checkers, passed. Changed-file Pylint and git diff --check passed.

Live-service and Docker validation remain with hosted CI.