Fix gRPC empty compressed response handling

[Copilot]

gRPC responses containing empty repeated fields could trigger a main-process zlib error (unexpected end of file) when the response frame was marked compressed but had a zero-length payload. This prevented Insomnia from displaying valid responses such as { "article_ids": [] }.

• gRPC decompression

  • Patch @grpc/grpc-js compression handling to treat compressed zero-length message payloads as valid empty buffers.
  • Apply the same handling for gzip and deflate paths.
  • Preserve normal decompression errors for malformed non-empty payloads.

• Regression coverage

  • Add coverage for receiving a compressed empty gRPC message frame without throwing.

const frame = Buffer.alloc(5);
frame.writeUInt8(1, 0);      // compressed
frame.writeUInt32BE(0, 1);   // zero-length payload

await expect(filter.receiveMessage(Promise.resolve(frame)))
  .resolves.toEqual(Buffer.alloc(0));

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