fix: when the task has started and did not download the data, gc is failed

[gaius-qi]

Description

This pull request includes updates to the garbage collection logic in the dragonfly-client project. The changes improve the handling of tasks based on their download status and content length.

Key updates to garbage collection logic:

• Enhanced logic to handle tasks with different download statuses, ensuring that tasks with finished downloads and valid content lengths have their space correctly evicted.
• Added conditions to skip tasks without content length unless the task has failed, in which case it logs the failure and assigns an evicted space of 0.

Related Issue

Motivation and Context

Screenshots (if appropriate)

[chlins]

lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.85%. Comparing base (41a1b34) to head (a32da2f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #915   +/-   ##
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  Coverage   34.85%   34.85%           
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  Files          60       60           
  Lines        9239     9239           
=======================================
  Hits         3220     3220           
  Misses       6019     6019           

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

[CormickKneey]

lgtm