[common] Fix double position advance in DataOutputSerializer.writeBytes

[LuciferYang]

Purpose

close #9519

DataOutputSerializer.writeBytes(String) wrote each byte through writeByte, which goes to write(int) and does this.buffer[this.position++] = ..., and then advanced the position by the string length a second time. After the call length() reported twice the bytes written, and the next write landed past a gap of untouched buffer, so the serialized output was longer than the data and carried whatever the array happened to hold. Removing the extra advance is the whole change.

The sibling writeChars(String) has the same shape, a resize followed by a loop of writeChar, and never had that line, which is the form this method should have had.

I audited every position update in the class while checking this: write(byte[], int, int), write(MemorySegment, int, int), writeChar, writeShort, writeInt, writeLong, writeUTF, skipBytesToWrite and write(DataInputView, int) each advance by exactly the bytes they wrote. writeBytes was the only one that did not.

Nothing in the repository calls this overload, so no Paimon code path changes behavior. It is part of the java.io.DataOutput contract that DataOutputView exposes, so the defect was visible to callers outside the repository.

Tests

DataOutputSerializerTest is new; the class had no test before. All three assert on getCopyOfBuffer(), which is cut at length(), so each one pins the length and the content together.

• testWriteBytesAdvancesPositionOnce: writeBytes("abc") leaves exactly a b c.
• testWriteBytesLeavesTheNextWriteInPlace: writeBytes("abc") then writeInt(42) leaves a b c 0 0 0 42, which is the assertion that catches a gap rather than just a wrong length.
• testWriteBytesAcrossAResize: starts from a two-byte buffer and writes six bytes, so the growth path runs during the call.

All three fail against the pre-fix code.

mvn -pl paimon-common test on JDK 8: 12467 tests, 0 failures, 0 errors. checkstyle, spotless, enforcer and rat run clean.

[LuciferYang]

The two UTCase and ITCase Spark 3.x jobs failed on a Maven Central transport error rather than on this change: the 2.12 job died in the Build Spark 3 with 2.12 step, before any test ran, on Could not transfer artifact org.apache.spark:spark-sql_2.12:jar:tests:3.5.8 from/to central: Connection reset, and the 2.13 job was cancelled by the matrix fail-fast. A re-run should clear both. This PR touches only paimon-common; locally mvn -pl paimon-common clean test is green on JDK 8: 12467 tests, 0 failures.