fix: handle binary strings properly in builtin_str function

[label-hook]

Summary

Fixes an issue where binary strings like b'GET' were being converted to their string representation "b'GET'" instead of being properly decoded to 'GET'. This caused HTTP requests to fail with 404 errors when method names were passed as binary strings.

Changes

• Modified builtin_str() function in requests/compat.py to detect binary strings (bytes) and decode them using UTF-8 encoding
• Maintains backward compatibility for regular strings, integers, and other types
• Ensures HTTP method names work correctly regardless of whether they're passed as strings or binary strings

Testing

The fix was verified to handle:

• Binary strings like b'GET' are properly decoded to 'GET'
• Regular strings remain unchanged
• Other types (int, None, etc.) are converted to strings as before
• Integration with sessions.py ensures HTTP methods work correctly when passed as binary strings

Closes #67

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Closes #67