Delta Kernel target writes column-mapping IDs with column mapping disabled

Translating an Iceberg schema with field IDs to Delta through the Kernel target produces a table that delta-rs 1.6.3 cannot open:

```
Kernel error: Schema error: Column mapping is not enabled but field 'id' is annotated with delta.columnMapping.id
```

`DeltaKernelSchemaExtractor.getFieldMetadata()` copies `InternalField.fieldId` into `delta.columnMapping.id`. The target does not enable `delta.columnMapping.mode`, and the resulting protocol remains reader 1 / writer 2. The same emission is present on current upstream `main`.

To reproduce:

1. Sync an Iceberg snapshot whose schema contains a `long` field named `id` with field ID 1 to a fresh Delta Kernel target.
2. Inspect the first Delta commit: `schemaString` contains `"metadata":{"delta.columnMapping.id":1}`, configuration has no `delta.columnMapping.mode`, and the protocol is `{"minReaderVersion":1,"minWriterVersion":2}`.
3. Open the output using Python `deltalake` 1.6.3: `DeltaTable(path)`. It fails with the error above before reading data.

Expected: omit column-mapping annotations when the target does not enable column mapping. Keep reader 1 / writer 2 for these tables. Source-side extraction of IDs from column-mapped Delta tables should continue to work.

Locally, removing the five-line ID propagation block lets delta-rs 1.6.3 open the translated table and read both rows from a synthetic Parquet fixture, with the protocol unchanged. Regression checks cover nested structs, arrays, maps, preserved UUID/comment metadata, and the committed protocol. The current Spark target already uses `SparkSchemaExtractor`, which does not emit these annotations.

Reference: [Delta column-mapping protocol](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#column-mapping).

Start at DeltaKernelSchemaExtractor.getFieldMetadata() and inspect the Delta target’s first commit generation, then reproduce the schema with an Iceberg field ID. Run the regression checks, including nested structs, arrays, maps, UUID/comment metadata, and protocol assertions; done means delta-rs 1.6.3 opens the output while reader 1 / writer 2 remains unchanged and source-side ID extraction still works.

Written by the indexing model from the issue text.