Slice 4: Fault-injection / instrumentation parity test harness

Parent PRD

#7331

What to build

A reusable fault-injection / instrumentation test wrapper built on the Lance-level wrapper surface that can fail or perturb a specific operation — a range read, writer shutdown, list, delete, or copy — regardless of backend. Demonstrate the same fault-injection test running on file:// and memory:// without resorting to file-object-store://.

Acceptance criteria

• Test wrapper can inject failures into: reader get_range, writer shutdown, list, delete, copy
• Same fault-injection test runs on local file:// and memory:// (no file-object-store://)
• Wrapper is reusable from other crates' tests (lives in a test-support location)
• At least one existing flaky/hard-to-test path gains a fault-injection test using it

Blocked by

• Blocked by #7332
• Blocked by #7333

Design sections addressed

• "Better Testing and Fault Injection"; Success criterion #3

Start by reviewing the Lance-level wrapper surface and the work in blocked issues #7332 and #7333. Build the reusable wrapper in a test-support location, then exercise fault injection for reader get_range, writer shutdown, list, delete, and copy against both file:// and memory://. Done means another crate can reuse it and at least one existing flaky or hard-to-test path has a fault-injection test.