fix: Bound decode_compressed to the length zlib actually wrote

[Mounika2456]

decode_compressed trusts the uncompressed size declared in the term header instead of the length uncompress() reports back, so a term that declares more than its zlib stream produces has the remainder decoded out of heap that was never written.

An ett_compressed term declaring 4096 bytes whose stream deflates to five (an ett_binary header announcing 4080 bytes of payload) comes back as a 4080 character string assembled from that memory; under ASAN the same input trips container-overflow in read_8_bits, since reserve() leaves the vector empty. zlibcontext::decompress already sizes its buffer and counts what inflate wrote, so this brings the term decoder in line with it. Covered by a new offline test that fails on master.

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[Mounika2456]

Superseded by #1623, which is this same branch raised against dev. GitHub won't let me reopen this one while that is open, so leaving it closed.