fix: close remaining FFI panic boundary gaps

[u70b3]

Follow-up to #62 and #61. This addresses the remaining lance_dataset_take / take_rows review note and the additional FFI boundary gaps found in a full post-merge audit.

Summary

• keep ordinary error formatting, TLS updates, and ABI sentinel construction inside the panic firewall; reject panic=abort builds
• guard materialized take / take_rows Arrow readers, preflight schemas, sanitize deferred errors, and contain release-time panics
• make scanner poisoning and output initialization consistent across setters and iteration APIs
• reject NULL async callbacks and poll wakers, make cloned RawWakers one-shot, and preserve exactly-once async completion when dispatcher startup or delivery fails
• add an explicit free API for library-allocated async Arrow stream containers and document C/C++ ownership
• guard index-segment metadata accessors and cleanup, and make C++ zero-sentinel wrappers check TLS immediately

Validation

• cargo fmt --check
• cargo check --all-targets --offline
• cargo clippy --all-targets --offline -- -D warnings
• cargo test --offline (346 tests passed)
• cargo test --test compile_and_run_test --offline -- --ignored (C and C++)
• cargo rustdoc --lib --offline -- -D warnings
• cargo check --release --all-targets --offline
• cargo rustc --lib --offline -- -C panic=abort (expected compile-time rejection)

No dependency or Cargo.lock changes.

[lance-gatekeeper]

✅ Gate recommendation: approve.

The panic-containment change remains well-grounded, and the previous poll-waker lifetime blocker is fixed. Scanner close now cancels pending registrations and waits for active callbacks before freeing the scanner, with registration serialized against retirement. The public lifetime/no-reentry contract and focused regressions cover retained-waker cancellation and active-callback quiescence.