aivis 1.2.1 — bounded reads

Security fix, second of two. Both fetch paths did an unbounded read. The gzip path was worse: decompression was unbounded, so a few hundred KB on the wire could become gigabytes in memory — a decompression bomb.

Demonstrated: a 204 KB payload expanding to 209 MB now caps at 8 MB. Covered in CI by a test that builds a real gzip bomb.

With 1.2.0's SSRF guard, both vulnerabilities were found by reading what competitors describe themselves as doing and checking whether it was true here.