Upsert with 1M rows extremely slow due to `create_match_filter` and `txn.delete()` performance

### Apache Iceberg version

0.11.0

### Please describe the bug 🐞

CC @goutamvenkat-anyscale @koenvo @Fokko

Hello! We are implementing distributed writes from Ray Data to Iceberg. As part of upserts, we:

1. Write data files in parallel across Ray workers (each worker writes its share of Parquet files directly to storage and returns `DataFile` metadata + the upsert key columns back to the driver)
2. On the driver, concatenate all upsert keys collected from workers, call `create_match_filter` to build a delete predicate, then call `txn.delete()` followed by an append to commit

Upserting 1M rows (383 MiB) into an Iceberg table takes **~17.5 minutes**, almost entirely in the delete step:

```
create_match_filter (1M keys → In filter): 10.26s
txn.delete(): 1054.35s
append + commit: 1.14s
─────────────────────────────────────────────────────
Total upsert commit: 1065.75s
```

PyIceberg version `0.11.0`

This matches what's reported in #2159 and #2138.

The bottlenecks are:
1. **`create_match_filter`** — constructs a Python `BooleanExpression` node per row, which is expensive at 1M+ keys
2. **`txn.delete()`** — evaluates the resulting giant `In` expression against the table's data files with no partition pruning, effectively doing a full table scan

We have a few questions:

1. **Merge-on-read upserts** — is this on the roadmap, and if so, roughly when? MoR would let us avoid the expensive delete + rewrite cycle entirely for large upserts.
2. **Optimizing `create_match_filter` or `txn.delete()`** — is there a recommended way to speed these up today? For example, batching the `In` filter, or passing a partition-level hint to constrain the file scan?
3. **Partition-aware deletes** — if the upsert key columns overlap with partition columns, is there a supported way to restrict `txn.delete()` to only the relevant partitions, rather than scanning the full table?

## Related

- #2159 — Upserting large table extremely slow
- #2138 — Upsertion memory usage grows exponentially as table size grows
- #2943 — Optimize upsert performance for large datasets

### Willingness to contribute

- [ ] I can contribute a fix for this bug independently
- [x] I would be willing to contribute a fix for this bug with guidance from the Iceberg community
- [ ] I cannot contribute a fix for this bug at this time

Beginne mit den im Bericht beschriebenen Einstiegspunkten create_match_filter und txn.delete(), und reproduziere anschließend den Upsert-Benchmark mit 1M Zeilen anhand der bereitgestellten Zeitmessungen. Sieh dir die verwandten Issues #2159, #2138 und #2943 an, um den bestehenden Kontext zu berücksichtigen. Die Arbeit ist abgeschlossen, wenn entweder eine gemessene Verbesserung oder eine dokumentierte, unterstützte Möglichkeit vorliegt, die gemeldeten Kosten des Löschens der gesamten Tabelle zu vermeiden.

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