feat: add parent selector with connection management and capacity control

[SouthWest7]

Description

This PR significantly enhances the parent selector functionality with robust connection management, reference counting, and capacity control mechanisms to improve reliability and resource utilization.

Related Issue

Tracing

Config

• model flie: Qwen3-0.6B
• parent1: upload_rate_limit = 20MiB
• parent2: upload_rate_limit = 10MiB
• hsot: download_rate_limit = 30MiB

origin

parent selector

Changes

New Features

• Bandwidth-based Selection: Selects optimal parent peers based on available upload bandwidth using weighted random selection.
• Dynamic Weight Calculation: Automatically calculates parent weights from real-time network statistics.
• Reference Counting: Automatic connection lifecycle management using RAII pattern with ConnectionGuard.

API Design

Core Methods

// Create new ParentSelector with configuration
pub fn new(config: Arc<Config>, id_generator: Arc<IDGenerator>) -> Result<ParentSelector>

// Register multiple parents for monitoring
pub async fn register_parents(&self, parents: &[CollectedParent]) -> Result<()>

// Get connection to specific parent with reference counting
pub async fn get_connection(&self, parent: &CollectedParent) -> Result<(ConnectionGuard, DfdaemonUploadClient)>

// Select optimal parent based on bandwidth weights
pub fn select_parent(&self, parents: Vec<CollectedParent>) -> Result<CollectedParent>

// Remove parents and cleanup connections
pub async fn unregister_parents(&self, parents: Vec<Peer>) -> Result<()>

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

Attention: Patch coverage is 52.20418% with 206 lines in your changes missing coverage. Please review.

Project coverage is 47.92%. Comparing base (d899d99) to head (a64205a).

Files with missing lines	Patch %	Lines
dragonfly-client/src/resource/parent_selector.rs	59.84%	151 Missing ⚠️
dragonfly-client/src/resource/task.rs	0.00%	22 Missing ⚠️
dragonfly-client/src/resource/piece_collector.rs	0.00%	19 Missing ⚠️
dragonfly-client/src/bin/dfdaemon/main.rs	0.00%	8 Missing ⚠️
dragonfly-client/src/grpc/dfdaemon_upload.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1161      +/-   ##
==========================================
+ Coverage   47.81%   47.92%   +0.11%     
==========================================
  Files          60       61       +1     
  Lines       14207    14629     +422     
==========================================
+ Hits         6793     7011     +218     
- Misses       7414     7618     +204     

Files with missing lines	Coverage Δ
dragonfly-client/src/grpc/dfdaemon_upload.rs	0.00% <0.00%> (ø)
dragonfly-client/src/bin/dfdaemon/main.rs	0.00% <0.00%> (ø)
dragonfly-client/src/resource/piece_collector.rs	0.00% <0.00%> (ø)
dragonfly-client/src/resource/task.rs	8.50% <0.00%> (-0.32%)	⬇️
dragonfly-client/src/resource/parent_selector.rs	59.84% <59.84%> (ø)

... and 1 file with indirect coverage changes

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