Add gzip compression for responses larger than 1KB

[ayo-ola0710]

📌 Summary

Implements gzip compression for REST and GraphQL responses to reduce network payload size (#320).

🚀 What was done

• Created a custom ConditionalGZipMiddleware in django-backend/soroscan/middleware.py.
• Inherited from Django's built-in GZipMiddleware to cleanly leverage standard compression logic while enforcing our specific threshold.
• Placed the middleware strategically within the MIDDLEWARE list in settings.py so it processes responses late in the request lifecycle.
• Included robust tests to verify the compression applies accurately.

🧠 Key Logic

• Conditional Compression: Hooked into the response processing to ensure we only compress payloads larger than 1KB. Small responses bypass the compression step to avoid CPU overhead and the situation where compression increases the payload size.
• Double Compression Avoidance: Leverages existing headers to check if the Content-Encoding header has already been set.
• Client Support Validation: Native Django middleware handles the Accept-Encoding: gzip requirement seamlessly.

🧪 Tests

• ✅ test_compresses_large_response: Verifies responses > 1KB get gzipped and have the correct headers.
• ✅ test_does_not_compress_small_response: Ensures responses < 1KB remain uncompressed to avoid performance impact.
• ✅ test_does_not_compress_if_already_compressed: Guarantees we do not double-compress an already gzipped response.

Closes #320

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