new feature: provides a way to control memory allocation and deallocation

### Feature Description

OpenDAL currently does not support allowing callers to take control of memory management, which is crucial for programs based on C and C++.

### Problem and Solution

Enable users to define a custom memory allocator that can replace the default Rust memory allocation mechanisms.

### Additional Context

_No response_

### Are you willing to contribute to the development of this feature?

- [X] Yes, I am willing to contribute to the development of this feature.

No files, tests, or entry points are named. Start by mapping the Rust allocation boundary and how C and C++ callers interact with OpenDAL, then clarify the allocator API and ownership expectations. Done means callers can define a custom allocator that replaces the default Rust allocation mechanisms.

Written by the indexing model from the issue text.