feat: coordinate parent selector and piece collector for better bandwidth usage

[SouthWest7]

Description

This PR improves bandwidth utilization during task downloads by enhancing the coordination between the Pparent Selector and the Piece Collector.

The piece collector is extended to

• proactively collect a sufficient number of parent peers,
• enabling the parent selector to make more effective scheduling decisions at download time.

In the presence of unstable parent peers, the implementation gracefully falls back to the previous behavior to maintain reliability.

Related Issue

dragonflyoss/dragonfly#3713

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.76%. Comparing base (2c4ad66) to head (59dc5be).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
dragonfly-client/src/resource/piece_collector.rs	0.00%	32 Missing ⚠️
dragonfly-client/src/resource/parent_selector.rs	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1578      +/-   ##
==========================================
- Coverage   42.84%   42.76%   -0.09%     
==========================================
  Files          75       75              
  Lines       21184    21268      +84     
==========================================
+ Hits         9077     9095      +18     
- Misses      12107    12173      +66     

Files with missing lines	Coverage Δ
dragonfly-client/src/resource/task.rs	7.33% <ø> (ø)
dragonfly-client/src/resource/parent_selector.rs	0.00% <0.00%> (ø)
dragonfly-client/src/resource/piece_collector.rs	0.00% <0.00%> (ø)

... and 4 files with indirect coverage changes

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[SouthWest7]

Test

Env

• Bandwidth: 1GiB
• Piece Concurrent: 16
• File Size: 30GiB
• Scenario: Single Task

Result

• Metrics: Completion Time (T1–T10)

Version	T1	T2	T3	T4	T5	T6	T7	T8	T9	T10
origin (left)	29s	86s	86s	86s	87s	87s	87s	87s	87s	89s
improved (right)	29s	49s	49s	49s	49s	49s	50s	50s	50s	50s