read: avoid repeated open and close for handle based services

OpenDAL's current raw read path models `Access::read(path, OpRead { range, .. })` as opening one concrete range stream.

This works naturally for HTTP object stores because each range read is a separate request. However, handle based services such as `fs`, `hdfs`, `sftp`, and `monoiofs` can reuse an opened handle and execute multiple positioned reads against it. The current core reader planner still calls `Access::read` for every planned range, so those services repeatedly open and close handles for workloads like `Reader::read`, `Reader::fetch`, chunked reads, and seek based async readers.

We should change the raw read contract so `Access::read(path, OpRead)` returns a reusable raw reader for the path and read condition set, and move byte ranges to methods on that returned reader.

Start with the raw read contract at Access::read(path, OpRead) and trace how the core reader planner uses it for each planned range. The change is complete when the returned raw reader can perform multiple byte-range reads, allowing handle-based services such as fs, hdfs, sftp, and monoiofs to reuse an opened handle.

Written by the indexing model from the issue text.