feat: add iperf3 for Dockerfile and change is_expired for PersistentCacheTask

[gaius-qi]

Description

This pull request includes changes to the ci/Dockerfile and the dragonfly-client-storage/src/metadata.rs file. The most important changes are the addition of a new package to the Dockerfile and the simplification of the expiration logic in the PersistentCacheTask implementation.

Dockerfile Update:

• ci/Dockerfile: Added iperf3 to the list of packages installed during the Docker image build process. This addition ensures that iperf3 is available in the Docker image for network performance testing.

PersistentCacheTask Logic Simplification:

• dragonfly-client-storage/src/metadata.rs: Simplified the expiration check in the is_expired method of the PersistentCacheTask struct by removing the additional time buffer previously used to force eviction. Now, the task is considered expired strictly based on the ttl value.

Related Issue

Motivation and Context

Screenshots (if appropriate)

[chlins]

lgtm

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 33.19%. Comparing base (a33f861) to head (c1fc4e9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dragonfly-client-storage/src/metadata.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #975      +/-   ##
==========================================
+ Coverage   33.18%   33.19%   +0.01%     
==========================================
  Files          59       59              
  Lines        9640     9637       -3     
==========================================
  Hits         3199     3199              
+ Misses       6441     6438       -3     

Files with missing lines	Coverage Δ
dragonfly-client-storage/src/metadata.rs	58.53% <0.00%> (+0.70%)	⬆️