GeezerVison

Fixes gh-41668.

Summary of Changes

When decompressing truncated gzip archives or streams ending unexpectedly before the trailer,
eadall()\ and \decompress()\ raised \EOFError\ while discarding all decompressed blocks accumulated prior to the EOF.

This patch:

1. Updates _streams.BaseStream.readall()\ to catch \EOFError\ on truncated reads and attach accumulated decompressed bytes as \�xc.partial_data\ before re-raising.
2. Updates \gzip.decompress()\ with \partial=False\ by default (preserving existing exception raising semantics), while returning decompressed payload if \partial=True.
3. Adds regression tests to \Lib/test/test_gzip.py\ validating both \partial=True\ recovery and \�xc.partial_data\ attachment.