Fix the 3 ignored tests covering a refused consumer-offset write

**After #4132 is merged.**

Each test below carries its reason in the `#[ignore]` attribute and its doc comment.

| Test | Location |
|---|---|
| `given_a_full_disk_when_the_offset_write_is_refused_then_persistence_should_not_fence` | `core/partitions/src/persistence.rs:1317` |
| `given_a_full_disk_when_driving_persistence_then_only_the_partition_should_fence` | `core/partitions/src/iggy_partition.rs:15167` |
| `given_a_divergent_prepare_when_submitting_then_the_partition_should_not_latch` | `core/partitions/src/iggy_partition.rs:15193` |

```
cargo test -p partitions --lib -- --ignored
```

Remove each `#[ignore]` once it passes. The third is marked contested in its doc comment — decide whether to fix it or delete it.

After #4132 is merged, run `cargo test -p partitions --lib -- --ignored`. Read the ignored tests in `core/partitions/src/persistence.rs:1317` and `core/partitions/src/iggy_partition.rs:15167,15193`, including their ignore reasons and doc comments. Done means the applicable tests pass without `#[ignore]`; resolve the contested third test by fixing it or deleting it.

Written by the indexing model from the issue text.