Fallback to Blob Response Body Size if No Content-Length

[Step7750]

Sometimes Content-Length isn't returned, so we want to fallback.

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Note

Low Risk
Low risk: change only affects response-size estimation and adds a safe fallback path when content-length is absent, though it now consumes the response body via blob() in that case.

Overview
Improves calculateResponseSize so it no longer throws when the response lacks a Content-Length header.

When content-length is missing, it now falls back to reading the response as a Blob and using blob.size to compute max_recv_data.

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