task(io): reuse storage operator in FileIO

[QuakeWang]

Search before asking

• I searched in the issues and found nothing similar.

Description

In PR #101, we intentionally scoped out the storage operator reuse part for easier review.

This issue tracks reusing OpenDAL Operator per FileIO instance in Rust Storage, instead of rebuilding one on every call. The goal is to improve consistency (especially for the memory backend across calls) and reduce unnecessary operator initialization overhead.

Reference from Java Paimon:

• ResolvingFileIO caches FileIO instances.
• PluginFileIO reuses lazy FileIO.
• HadoopFileIO caches FileSystem instances.

Willingness to contribute

• I'm willing to submit a PR!