compression: empty input marks BZ2/LZMA decompressors as EOF #8637

Summary

Calling decompress(b"") before compressed input marks BZ2Decompressor
and LZMADecompressor as finished.

Expected

Empty input should be a no-op. CPython keeps eof false and needs_input
true, then accepts compressed data supplied by a later call:

BZ2Decompressor False True
b'data'
LZMADecompressor False True
b'data'

Actual

RustPython marks both decompressors as finished and rejects a later input:

BZ2Decompressor True False
EOFError: End of stream already reached
LZMADecompressor True False
EOFError: End of stream already reached

Python Documentation

• https://docs.python.org/3/library/bz2.html#bz2.BZ2Decompressor
• https://docs.python.org/3/library/lzma.html#lzma.LZMADecompressor