fix(http): skip caching relative 307 redirect locations and resolve them

[gaius-qi]

Description

This pull request improves how HTTP 307 Temporary Redirects are handled and cached in the dragonfly-client-backend. The main focus is to ensure that only absolute URLs are cached as redirect targets, preventing potential issues with relative URLs. Additionally, a new test verifies this behavior.

Redirect handling and caching improvements:

• Updated logic in store_temporary_redirect_url to skip caching redirects when the Location header is a relative URL, logging a debug message in such cases. Only absolute URLs are now cached as valid redirect targets.
• Added a debug log after successfully caching a temporary redirect, making it easier to trace caching behavior.

Redirect resolution and request flow:

• Changed how redirect URLs are resolved: now, relative Location headers are joined with the base URL to form an absolute URL before following the redirect. However, only the original Location value (not the resolved absolute URL) is considered for caching, aligning with the new caching logic. This change is applied in both the stat and get request flows. [1] [2]

Testing:

• Added a new async test should_not_cache_relative_307_redirect_location to verify that relative redirect URLs are not cached, ensuring the origin server is contacted again for subsequent requests.

Related Issue

Fixed dragonflyoss/dragonfly#4710

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

❌ Patch coverage is 97.26027% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.66%. Comparing base (5400d49) to head (8c55fa2).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dragonfly-client-backend/src/http.rs	97.26%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1777      +/-   ##
==========================================
+ Coverage   44.54%   44.66%   +0.12%     
==========================================
  Files          91       91              
  Lines       25834    25905      +71     
==========================================
+ Hits        11508    11571      +63     
- Misses      14326    14334       +8     

Files with missing lines	Coverage Δ
dragonfly-client-backend/src/http.rs	97.11% <97.26%> (+0.13%)	⬆️

... and 1 file with indirect coverage changes

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