Move gzip import to module level in middleware

[Copilot]

Addresses code review feedback to follow Python convention of importing standard library modules at the module level rather than inside functions.

Changes

• Moved import gzip from inside _inject_toolbar() method to top-level imports alongside other standard library modules
• No functional changes—all existing gzip operations (decompress(), compress(), BadGzipFile) continue to work identically

# Before: import inside method
def _inject_toolbar(self, body: bytes, ...) -> tuple[bytes, str]:
    import gzip
    body = gzip.decompress(body)
    
# After: module-level import
import gzip

def _inject_toolbar(self, body: bytes, ...) -> tuple[bytes, str]:
    body = gzip.decompress(body)

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