Fix gzip response handling to preserve HTTP semantics on decode failure

[Copilot]

When a gzipped response decompresses successfully but contains non-UTF-8 bytes, the middleware was returning decompressed binary data with no content-encoding header. This violates HTTP semantics—the client requested gzip via Accept-Encoding but received uncompressed binary.

Changes

• Store original body before decompression: Added original_body to preserve the compressed payload
• Return original on decode failure: When UTF-8 decoding fails, return original_body with original content_encoding instead of decompressed bytes with empty encoding
• Simplify exception handling: Removed unused decompressed flag, use contextlib.suppress for cleaner code

Example

Before:

# Client requests gzipped response
# Middleware decompresses successfully but decode fails
# Returns: decompressed binary + content-encoding: ""
# Result: Client receives unexpected format

After:

# Client requests gzipped response  
# Middleware decompresses successfully but decode fails
# Returns: original compressed body + content-encoding: "gzip"
# Result: Client receives expected format

The middleware now respects the client's Accept-Encoding negotiation when toolbar injection isn't possible.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: /usr/bin/curl curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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