* common: share the zlib stream engine
Move the VM-independent zlib-rs stream owner and state machine into a feature-gated rustpython-common module. Make rustpython-stdlib adapt that engine instead of carrying its own flate2 implementation, including native stream copy/deepcopy, Z_BLOCK flushes, and wbits=0 decompression.
Assisted-by: Codex:GPT-5
* common: share the lzma stream engine
Move the VM-independent liblzma stream owner, filter properties, and compression state into a target-gated rustpython-common module. Keep rustpython-stdlib as the Python object and exception adapter, and remove its direct xz dependencies and lzma-only generic compressor machinery.
Assisted-by: Codex:GPT-5
* common: address compression engine reviews
- add a special_retrieve fudge function to the PyValue trait
- define the special_retrieve function for PyInt
- remove blocks on successful tests to reflect effect of changes