Bound HTTP/1 body reads.

[samuel-williams-shopify]

Fixed-length and chunked bodies now return at most 64 KiB from each read, independently of the underlying stream implementation.

Chunked bodies retain the remaining transfer chunk length across reads, allowing upper layers to enforce total representation limits without first buffering an entire adversarial transfer chunk. Chunk terminators are now validated strictly, and truncated chunks close the read side before raising EOFError.

The declared HTTP transfer chunk size remains unrestricted because transfer chunk boundaries do not carry representation semantics.

Tests cover bounded fixed and chunked reads, invalid chunk terminators, and incremental truncation handling.