Fix javadoc warnings

[heuermh]

Javadoc warnings

    [INFO] --- javadoc:3.5.0:jar (attach-javadocs) @ duckdb-parquet-tools ---
    [INFO] No previous run data found, generating javadoc.
    [WARNING] Javadoc Warnings
    [WARNING] warning: The code being documented uses modules but the packages defined in https://docs.oracle.com/javase/8/docs/api/ are in the unnamed module.
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/target/generated-sources/java-templates/com/github/heuermh/duckdb/parquet/tools/About.java:23: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class About implements IVersionProvider {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Convert.java:34: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Convert implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Create.java:34: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Create implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Describe.java:39: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Describe implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Head.java:43: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Head implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Meta.java:39: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Meta implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Schema.java:39: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Schema implements Callable<Integer> {
    [WARNING] ^
    [WARNING] /Users/heuermh/working/duckdb-parquet-tools/src/main/java/com/github/heuermh/duckdb/parquet/tools/Tools.java:49: warning: use of default constructor, which does not provide a comment
    [WARNING] public final class Tools {
    [WARNING] ^
    [WARNING] 9 warnings