fix(java): type scanner operation failures

[lance-gatekeeper]

Summary

• add a documented LanceException unchecked exception for operation failures
• wrap synchronous and asynchronous scanner failures with the typed exception
• cover the native async failure callback with a regression test

Root cause

LanceScanner and AsyncScanner converted scanner I/O and native-operation failures into bare RuntimeException instances. Callers therefore could not distinguish Lance operation failures from unrelated programming errors.

Validation

• ./mvnw -Dtest=AsyncScannerTest#testNativeScanFailureUsesLanceException test (passes; JNI Rust unit tests also pass)
• ./mvnw spotless:check (passes)
• cargo fmt --manifest-path ./lance-jni/Cargo.toml --all (passes)
• ./mvnw -Djava.io.tmpdir=/home/repo/java/target/test-tmp test (397 passed, 26 skipped; one existing forked-JVM classloader test fails because its child JVM extracts JNI libraries to the non-executable /tmp mount)

Fixes #7611

[lance-gatekeeper]

✅ Gate recommendation: approve.

The change establishes a compatible typed failure boundary for synchronous stream creation and asynchronous native/import failures while preserving available causes and leaving programming-state exceptions distinct. A checked exception cannot fit Arrow’s Scanner override or CompletableFuture, and a global JNI remap would alter unrelated APIs, so the focused Java-boundary wrapper is the preferable mechanism.