HashJoinExec `probe_hit_rate` metric overcounts probe rows when a probe batch is processed in several chunks

## Describe the bug

The `probe_hit_rate` metric of `HashJoinExec` is documented as "fraction of probe-side rows with a build-side join-key match before applying any join filter", but its denominator is inflated whenever a probe batch is processed in more than one chunk.

`HashJoinStream::process_probe_batch` adds `state.batch.num_rows()` to the metric's total at the top of the function:

https://github.com/apache/datafusion/blob/a5c809f98/datafusion/physical-plan/src/joins/hash_join/stream.rs#L763-L765

When the hash-map lookup hits `batch_size` output rows before the probe batch is exhausted, `process_probe_batch` returns with `next_offset` set and is re-entered for the *same* probe batch. Each re-entry adds the full batch row count again, so a probe batch that produces `k` chunks is counted `k` times in the denominator.

The numerator has a smaller version of the same problem: `add_part(distinct_right_indices_count)` counts the distinct probe indices of each chunk, so a probe row whose match chain is split across two chunks is counted twice.

## To Reproduce

Run any hash join whose fanout makes the output exceed `batch_size` per probe batch, e.g. a build side with many duplicate keys, and inspect the metric with `EXPLAIN ANALYZE`. A 4-row probe batch with 8 matches each and `batch_size = 8` produces 4 chunks, so the metric reports a total of 16 probe rows instead of 4 and a hit rate of 0.25 instead of 1.0.

## Expected behavior

Both counters should reflect each probe row once: the total should be added once per probe batch (for example only when `state.offset == (0, None)`), and a probe row spanning a chunk boundary should not be counted twice in the part.

## Additional context

Found while reviewing `process_probe_batch` in `datafusion/physical-plan/src/joins/hash_join/stream.rs`. `avg_fanout` uses `distinct_right_indices_count` as its total and has the same chunk-boundary double count, though its part (`left_indices.len()`) is correct.