feat: set permissions for Unix Domain Socket in dfdaemon_download

[gaius-qi]

Description

This pull request includes changes to the dragonfly-client to enhance the handling of Unix domain sockets and permissions.

Enhancements to Unix domain sockets and permissions:

• dragonfly-client/src/grpc/dfdaemon_download.rs: Added import for PermissionsExt from std::os::unix::fs to handle Unix file permissions.
• dragonfly-client/src/grpc/dfdaemon_download.rs: Added code to set permissions for the Unix domain socket to 0o660 after binding it, ensuring proper access control.

Related Issue

dragonflyoss/dragonfly#3811

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 33.07%. Comparing base (04c71e6) to head (fa7bb66).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #981   +/-   ##
=======================================
  Coverage   33.07%   33.07%           
=======================================
  Files          59       59           
  Lines        9741     9741           
=======================================
  Hits         3222     3222           
  Misses       6519     6519           

Files with missing lines	Coverage Δ
dragonfly-client/src/grpc/dfdaemon_download.rs	0.00% <ø> (ø)

[chlins]

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