chore: update lance dependency to v6.0.0-beta.7 (#3334)

## Summary
- Update Lance Rust dependencies to `6.0.0-beta.7` using
`ci/set_lance_version.py`.
- Update Java `lance-core.version` to `6.0.0-beta.7`.
- Align Arrow/DataFusion/PyO3 dependency versions and apply required
compatibility fixes for the Lance upgrade.

Triggering tag:
[v6.0.0-beta.7](https://github.com/lance-format/lance/releases/tag/v6.0.0-beta.7)

## Verification
- `cargo clippy --workspace --tests --all-features -- -D warnings`
- `cargo fmt --all`

python/src/header.rs

@@ -33,7 +33,7 @@ impl PyHeaderProvider {
                 Ok(headers_py) => {
                     // Convert Python dict to Rust HashMap
                     let bound_headers = headers_py.bind(py);
-                    let dict: &Bound<PyDict> = bound_headers.downcast().map_err(|e| {
+                    let dict: &Bound<PyDict> = bound_headers.cast().map_err(|e| {
                         format!("HeaderProvider.get_headers must return a dict: {}", e)
                     })?;