test: add unit tests for calculate_piece_range

[gaius-qi]

Description

This pull request includes several changes aimed at refactoring the code for calculating piece ranges and improving the test coverage. The main changes involve extracting the calculate_piece_range function into a standalone function and updating the related code to use this new function.

Refactoring and code improvement:

• dragonfly-client-storage/src/content.rs: Extracted the logic for calculating the target offset and length based on the range into a new function calculate_piece_range. This function is now called in the impl Content block instead of the inline logic. [1] [2] [3]
• dragonfly-client/src/proxy/cache.rs: Similarly, extracted the logic for calculating the target offset and length into the calculate_piece_range function and updated the impl Cache block to use this function. [1] [2] [3]

Test coverage:

• Added unit tests for the calculate_piece_range function in both dragonfly-client-storage and dragonfly-client to ensure the correctness of the calculations. [1] [2]

Dependency update:

• dragonfly-client-storage/Cargo.toml: Added tempfile.workspace = true to the dev-dependencies section to support the new tests.

Minor improvement:

• dragonfly-client/src/proxy/mod.rs: Added a comment to clarify the logic for adding a piece to the cache when the piece reader reaches the end.

Related Issue

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

Attention: Patch coverage is 97.57576% with 4 lines in your changes missing coverage. Please review.

Project coverage is 34.85%. Comparing base (6ace03a) to head (9bc633a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dragonfly-client/src/proxy/cache.rs	95.29%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #907      +/-   ##
==========================================
+ Coverage   33.63%   34.85%   +1.21%     
==========================================
  Files          60       60              
  Lines        9095     9239     +144     
==========================================
+ Hits         3059     3220     +161     
+ Misses       6036     6019      -17     

Files with missing lines	Coverage Δ
dragonfly-client-storage/src/content.rs	38.53% <100.00%> (+35.63%)	⬆️
dragonfly-client/src/proxy/mod.rs	0.00% <ø> (ø)
dragonfly-client/src/proxy/cache.rs	55.47% <95.29%> (+55.47%)	⬆️

[chlins]

lgtm