MINOR: Fix PrimitiveStringifier class Javadoc to link UnsupportedOperationException

[anxkhn]

Rationale for this change

The class-level Javadoc of the public abstract class PrimitiveStringifier
(parquet-column/src/main/java/org/apache/parquet/schema/PrimitiveStringifier.java)
documents the wrong exception type. It states:

The overloaded methods not implemented for the related types throw
{@link OperationNotSupportedException}.

That {@link} resolves to javax.naming.OperationNotSupportedException, which is
the only reason the import javax.naming.OperationNotSupportedException; exists in
the file. Two problems follow from this:

1. Every stringify(...) overload that is not implemented for a type actually
   throws java.lang.UnsupportedOperationException, and each method's own
   @throws tag already documents UnsupportedOperationException. So the
   class-level contract contradicts every per-method contract in the same file.
2. javax.naming.OperationNotSupportedException is a checked exception
   (extends NamingException extends Exception). The unchecked stringify(...)
   methods cannot declare or throw it, so the documented behavior is impossible
   and would mislead a caller into catching the wrong exception type.

What changes are included in this PR?

A documentation-only change in one file:

• Point the class Javadoc {@link} at java.lang.UnsupportedOperationException
  (no import needed), so the class contract matches the six per-method @throws
  tags and the actual throw statements.
• Remove the now-unused import javax.naming.OperationNotSupportedException;,
  which existed solely to satisfy the incorrect link.

No behavioral change. Net diff is one import line removed and one word changed in
the Javadoc.

Are these changes tested?

This is a Javadoc/import-only change with no runtime behavior change, so no new
test is added. It was validated locally on parquet-column (JDK 21, Maven 3.9):

• mvn -pl parquet-column -Dspotless.check.skip=true -DskipTests compile succeeds,
  confirming the removed javax.naming import was unused.
• mvn -pl parquet-column javadoc:javadoc succeeds with no "reference not found"
  warning for PrimitiveStringifier; the generated HTML now links the class
  description to java.lang.UnsupportedOperationException and contains no
  javax.naming reference.
• mvn -pl parquet-column spotless:check succeeds (0 files need reformatting).
• mvn -pl parquet-column -Dtest=TestPrimitiveStringifier test passes
  (13 tests, 0 failures), confirming no behavioral change.

Are there any user-facing changes?

No. This only corrects Javadoc and removes a dead import. There is no API or
behavior change.

---

Notes for the ship step (not part of the PR body)

• Title uses MINOR: because there is no filed GitHub issue. This is explicitly
  sanctioned by .github/PULL_REQUEST_TEMPLATE.md ("or simply use the title below
  if it is a minor issue: MINOR: ${SUMMARY}") and matches recent master history
  (e.g. "MINOR: Fix error message in SimpleGroup.add() for binary (MINOR: Fix error message in SimpleGroup.add() for Binary #3385)").
• Do NOT uncomment the template's "Closes #${GITHUB_ISSUE_ID}" line: there is no
  issue to close.
• Rebase again onto origin/master right before pushing if upstream has advanced.
• Suggested PR branch name for the fork at ship time (the local patch-1 is just
  a placeholder): fix/primitivestringifier-javadoc-link.

[nastra]

LGTM