Fix issue #232: Handle size mismatch after file copy

[CatalinaLeca]

Title

If this is related to a GitHub issue, please have use the issue's title, inlcude #ID too.

Description

Please include a summary of the changes and the related issue. Describe why this change is needed.

Fixes # (issue)

---

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

---

Checklist:

• I have performed a self-review of my code
• I have tested my code on different platforms (if applicable)
• I have commented my code, particularly in hard-to-understand areas
• I have added necessary documentation (if appropriate)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

---

Screenshots (if applicable)

Add screenshots to illustrate changes if necessary.

---

Additional Context

Add any additional context or information here.

[Copilot]

Pull Request Overview

This PR addresses issue #232 by refining the write method to correctly handle size mismatches after file copy operations.

• Introduces a mutable offset and uses a looping mechanism to continue writing in chunks until the entire buffer is processed.
• Implements improved file handle validation and aggregates the total bytes written to update file attributes accordingly.

Comments suppressed due to low confidence (1)

src/encryptedfs.rs:1681

• The variable 'write_guard' is undefined. It should be replaced with the existing 'guard' variable or removed if not needed.

drop(write_guard);