Fix return value bug and improve test coverage to 94.1%

[Copilot]

Summary

Fixed a critical bug in the Test() method and significantly improved test coverage from 82.4% to 94.1%, exceeding the 80% requirement.

Bug Fix

The Test() method in http.go had a bug where it would return the err variable instead of nil on successful HTTP responses:

// Before (buggy)
func (h *HTTP) Test(ctx context.Context) error {
    // ... success path ...
    return err  // Bug: returns err instead of nil
}

// After (fixed)
func (h *HTTP) Test(ctx context.Context) error {
    // ... success path ...
    return nil  // Correct: explicitly return nil on success
}

This bug could potentially cause successful HTTP requests to be treated as errors in edge cases where err retained a non-nil value from previous operations.

Test Coverage Improvements

Added comprehensive test cases to cover previously untested code paths:

• TestNew_NilURL: Tests error handling when New() is called with a nil URL parameter
• TestHTTP_NetworkError: Tests network connection failure scenarios
• TestHTTP_InternalServerError: Tests HTTP 5xx server error responses
• TestHTTP_RedirectStatusCode: Tests HTTP 3xx redirect handling (validates they're treated as successful)

Results

• Coverage: 82.4% → 94.1% (exceeds 80% requirement)
• Function coverage:
  • Use(): 100.0% (unchanged)
  • New(): 66.7% → 100.0%
  • Test(): 84.6% → 92.3%
• Quality: All linting, vet, staticcheck, and race detection tests pass
• Tests: 8/8 test cases pass (4 existing + 4 new)

The remaining 5.9% uncovered code consists of extremely rare edge cases that are difficult to reproduce in testing (such as http.NewRequest failing with a valid URL, or response bodies being nil in specific HTTP scenarios).

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