fix(humafiber): correct Fiber v2 EachHeader iteration and body decompression - #1058

Fixes #1055

Problem

The Fiber v2 adapter (humafiber.NewV2, added in #962) has two bugs in its huma.Context implementation:

1. EachHeader iterates bytes, not headers. (*fasthttp.RequestHeader).All() returns iter.Seq2[[]byte, []byte] yielding (name, value) pairs, but the code treated the value as a slice of values and ranged over it, invoking the callback once per byte. A request with Authorization: Bearer abc produced ten single-character callbacks. This broke huma.ReadCookie/huma.ReadCookies, which collect the Cookie header via EachHeader, so cookies were no longer found.

2. BodyReader used BodyRaw() instead of Body(). BodyRaw() returns the raw bytes without decompressing, so compressed request bodies reached handlers still compressed. The Fiber v3 adapter and v2.37.3 both use Body(), which decompresses per Content-Encoding.

Fix

• EachHeader: range both values of the Seq2, one callback per header value.
• BodyReader: use orig.Body(), matching the v3 adapter and v2.37.3.

Tests

• TestFiberV2EachHeaderAndCookie — asserts one callback per header value and a readable cookie.
• TestFiberV2BodyReaderDecompresses — sends a gzip body with Content-Encoding: gzip and asserts the handler receives decompressed, parseable JSON.

Both tests fail against the unfixed source and pass with the fix.