Source-distribution builds leave `${buildNumber}` unresolved in version metadata

Building Parquet directly from the ASF source distribution cannot obtain the Git revision because the archive contains no `.git` metadata. Maven records a null `buildNumber`, leaving the placeholder unresolved in generated version information.

### Reproduction

Download and extract the source tarball from the [1.18.0 RC1 directory](https://dist.apache.org/repos/dist/dev/parquet/apache-parquet-1.18.0-rc1/), then run:

```bash
./mvnw -f parquet-generator/pom.xml package -DskipTests

tmp_dir=$(mktemp -d)
java -cp parquet-generator/target/parquet-generator-1.18.0.jar \
org.apache.parquet.version.VersionGenerator "$tmp_dir"

grep FULL_VERSION "$tmp_dir/org/apache/parquet/Version.java"
```

Result:

```text
parquet-mr version 1.18.0 (build ${buildNumber})
```

The JAR manifest’s `git-SHA-1` entry is also blank. In contrast, the [staged Maven JARs](https://repository.apache.org/content/repositories/orgapacheparquet-1081/org/apache/parquet/) correctly contain RC1 commit [`5e2ad0969c7f411613671c5ef054d399995de5f9`](https://github.com/apache/parquet-java/commit/5e2ad0969c7f411613671c5ef054d399995de5f9).

This also reproduces with the official [1.17.0 source distribution](https://archive.apache.org/dist/parquet/apache-parquet-1.17.0/), while the published 1.17.0 Maven JARs correctly contain release commit `fac0c746532e133beb928a7f6a7e57b510b477a1`. Therefore, this predates 1.18.0 and is not an RC1 regression.

### Impact

Source-built artifacts have incomplete or misleading provenance:

- `Version.FULL_VERSION` contains the unresolved placeholder.
- Parquet files written by those artifacts may include it in `created_by`.
- The manifest lacks the Git SHA.
- Source-built and staged artifacts report different build identities.

The build should embed the release commit or use an explicit fallback rather than emitting an unresolved Maven expression.

Relevant source: [`parquet-version.properties`](https://github.com/apache/parquet-java/blob/apache-parquet-1.18.0-rc1/parquet-generator/src/main/resources/parquet-version.properties).

Start with parquet-generator/src/main/resources/parquet-version.properties and reproduce the issue with the provided ./mvnw command and VersionGenerator invocation. Inspect the generated Version.java and JAR manifest; done means source-distribution builds no longer emit the unresolved ${buildNumber} placeholder and include the appropriate build identity.

Written by the indexing model from the issue text.