fix beacon chain download speed

[sparrowDom]

Node's fetch defaults to accept-encoding: gzip, deflate, which makes Lighthouse gzip the ~330MB state and drop content-length. Inflating that on the main thread backpressures the socket down to ~2 Mbps (a 15min download that hits the abort below), and the missing content-length also forces the slow chunk-accumulation path further down. Asking for identity doubles the wire bytes but the transfer takes ~2s.

Code Change Checklist

To be completed before internal review begins:

• The contract code is complete
• Executable deployment file
• Fork tests that test after the deployment file runs
• Unit tests *if needed
• The owner has done a full checklist review of the code + tests

Internal review:

• Two approvals by internal reviewers