【WIP】[common][filesystem] Add FileIO contract suite

[sundapeng]

What changed

This PR defines the FileIO behavior used by Paimon and runs the same contract tests against Local, Hadoop-local, HDFS, and S3.

• Add a FileIO API page covering all 37 public methods and Paimon's current call patterns.
• Test shared behavior, default helpers, and caller preconditions.
• Correct the mkdirs Javadoc: an existing directory returns true.
• Fix mismatches found in no-overwrite copy, atomic creation, two-phase cleanup and rollback, and S3 multipart initialization.

Scope

There are no public API signature changes, implementation flags, or Hadoop/POSIX compatibility claim. The existing FileIOBehaviorTestBase is unchanged. Ambiguous rename cases, listing order, pre-close visibility, exact timestamp precision, and backend request counts remain outside the shared contract.

Testing

• LocalFileIOBehaviorTest and HadoopLocalFileIOBehaviorTest: 127 tests.
• S3MultiPartUploadTest and S3AtomicWriteTest: 5 tests.
• Spotless checks and the Docusaurus production build passed locally.