fix: cross-platform test compatibility

[theRealThomasDavidson]

This PR fixes various cross-platform compatibility issues in tests, particularly between Windows and Unix-like systems.

Changes Made:

1. Path Separator Handling:

• Added filepath.ToSlash() for error message comparison and import map paths in deploy_test.go
• Added filepath.ToSlash() conversion for URL paths in storage operations
• Normalized path comparisons using filepath.ToSlash() for cross-platform compatibility in deno_test.go

2. Line Ending Normalization:

• Added comprehensive string normalization for form comparisons in upload_test.go:
  • Path separator normalization
  • Line ending normalization (\r\n -> \n)
  • Consecutive newline normalization
  • Backslash escaping normalization
• Added line ending normalization for diff comparisons in squash_test.go
• Added normalizeLineEndings() helper function in auth_test.go and token_test.go

3. Test Data Handling:

• Replaced testImports with in-memory filesystem setup using afero.NewMemMapFs()
• Added proper path handling for test file creation

Testing:

• Verified tests pass on both Windows and Unix systems
• Ensured URL paths consistently use forward slashes
• Confirmed line ending normalization works across platforms

Related Issue:

Fixes #3158