Tweak optimal default batch size

### Is your feature request related to a problem or challenge?

A small test to double the batch size (from 8192 to 16384) shows some performance improvements (~10%) on some queries:
```
Comparing main and batch_size
--------------------
Benchmark tpch_mem.json
--------------------
┏━━━━━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━━━┳━━━━━━━━━━━━━━━┓
┃ Query ┃ main ┃ batch_size ┃ Change ┃
┡━━━━━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━━━╇━━━━━━━━━━━━━━━┩
│ QQuery 1 │ 190.81ms │ 186.92ms │ no change │
│ QQuery 2 │ 59.14ms │ 55.43ms │ +1.07x faster │
│ QQuery 3 │ 47.03ms │ 44.95ms │ no change │
│ QQuery 4 │ 37.16ms │ 33.60ms │ +1.11x faster │
│ QQuery 5 │ 95.66ms │ 86.47ms │ +1.11x faster │
│ QQuery 6 │ 10.47ms │ 8.93ms │ +1.17x faster │
│ QQuery 7 │ 196.26ms │ 192.92ms │ no change │
│ QQuery 8 │ 69.94ms │ 63.64ms │ +1.10x faster │
│ QQuery 9 │ 136.17ms │ 129.56ms │ no change │
│ QQuery 10 │ 99.69ms │ 97.21ms │ no change │
│ QQuery 11 │ 45.22ms │ 45.94ms │ no change │
│ QQuery 12 │ 67.66ms │ 65.41ms │ no change │
│ QQuery 13 │ 182.43ms │ 156.67ms │ +1.16x faster │
│ QQuery 14 │ 12.36ms │ 11.16ms │ +1.11x faster │
│ QQuery 15 │ 23.18ms │ 20.79ms │ +1.11x faster │
│ QQuery 16 │ 48.14ms │ 47.22ms │ no change │
│ QQuery 17 │ 681.34ms │ 682.63ms │ no change │
│ QQuery 18 │ 516.47ms │ 490.86ms │ no change │
│ QQuery 19 │ 58.40ms │ 56.68ms │ no change │
│ QQuery 20 │ 193.13ms │ 202.12ms │ no change │
│ QQuery 21 │ 261.12ms │ 242.51ms │ +1.08x faster │
│ QQuery 22 │ 27.81ms │ 28.08ms │ no change │
└──────────────┴──────────┴────────────┴───────────────┘
```

This is nice for such a small change and aligns with https://github.com/apache/arrow-datafusion/issues/6287

### Describe the solution you'd like

Configure a (more) optimal default

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating the default batch-size configuration and the benchmark that uses tpch_mem.json; the issue's comparison provides the baseline for evaluating 8192 versus 16384. Done means selecting and configuring a justified default, then checking the benchmark results for improvements and regressions across the listed queries.

Written by the indexing model from the issue text.