Set adapter to be net_http instead of Faraday.default_adapter.

[jkogara]

What this does

It updates the Faraday middleware to specifically use the :net_http adapter instead of whatever the environment default is/was.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • All tests pass: bundle exec rspec
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

Related issues

Fixes #428

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.58%. Comparing base (a74233f) to head (2ae3d54).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #429   +/-   ##
=======================================
  Coverage   84.58%   84.58%           
=======================================
  Files          37       37           
  Lines        1933     1933           
  Branches      500      500           
=======================================
  Hits         1635     1635           
  Misses        298      298           

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