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/index.rs

@@ -13,7 +13,7 @@ use pyo3::{
     Bound, FromPyObject, PyAny, PyResult, Python,
     exceptions::{PyKeyError, PyValueError},
     intern, pyclass, pymethods,
-    types::PyAnyMethods,
+    types::{PyAnyMethods, PyString},
 };
 
 use crate::util::parse_distance_type;
@@ -22,7 +22,7 @@ pub fn class_name(ob: &'_ Bound<'_, PyAny>) -> PyResult<String> {
     let full_name = ob
         .getattr(intern!(ob.py(), "__class__"))?
         .getattr(intern!(ob.py(), "__name__"))?;
-    let full_name = full_name.downcast()?.to_string_lossy();
+    let full_name = full_name.cast::<PyString>()?.to_string_lossy();
 
     match full_name.rsplit_once('.') {
         Some((_, name)) => Ok(name.to_string()),