[GO-2023-2382] Denial of service via chunk extensions in net/http

A malicious HTTP sender can use chunk extensions to cause a receiver reading
from a request or response body to read many more bytes from the network than
are in the body.

A malicious HTTP client can further exploit this to cause a server to
automatically read a large amount of data (up to about 1GiB) when a handler
fails to read the entire body of a request.

Chunk extensions are a little-used HTTP feature which permit including
additional metadata in a request or response body sent using the chunked
encoding. The net/http chunked encoding reader discards this metadata. A sender
can exploit this by inserting a large metadata segment with each byte
transferred. The chunk reader now produces an error if the ratio of real body to
encoded bytes grows too small.