Add cache policy flag and cache management commands

[httpdss]

Summary

• add --cache-policy flag for remote content fetching with always, never and refresh modes
• introduce struct cache command to inspect or clear cached files
• document cache usage and policy options

Testing

• pytest -q

---

https://chatgpt.com/codex/tasks/task_e_6897de1045008323a89cb2f940bbfe10

[codecov]

Codecov Report

❌ Patch coverage is 58.27338% with 58 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.05%. Comparing base (42219a2) to head (d238c99).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
struct_module/content_fetcher.py	15.78%	48 Missing ⚠️
struct_module/commands/cache.py	62.50%	6 Missing and 3 partials ⚠️
struct_module/commands/generate.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
+ Coverage   67.98%   68.05%   +0.06%     
==========================================
  Files          26       28       +2     
  Lines        1718     1850     +132     
  Branches      222      240      +18     
==========================================
+ Hits         1168     1259      +91     
- Misses        496      530      +34     
- Partials       54       61       +7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.