Support headerless format in getFrameParameters and decompress

[swehner]

Adding support for magic-less format in a few functions:

• Add optional paramater format to get_frame_paramaters and switch to using getFrameHeader_advanced internally
• Use getFrameHeader_advanced in decompress instead of getFrameContentSize

Testing done:

$ export ZSTD_SLOW_TESTS=1  

$ for i in cext rust cffi; do echo "=== PYTHON_ZSTANDARD_IMPORT_POLICY=$i python setup.py test"; PYTHON_ZSTANDARD_IMPORT_POLICY=$i python setup.py test; done 2>&1 | grep "\(==\|OK\|Ran\|failed\|ERROR\)"
=== PYTHON_ZSTANDARD_IMPORT_POLICY=cext python setup.py test
Ran 292 tests in 13.942s
OK
=== PYTHON_ZSTANDARD_IMPORT_POLICY=rust python setup.py test
Ran 292 tests in 15.512s
OK
=== PYTHON_ZSTANDARD_IMPORT_POLICY=cffi python setup.py test
Ran 292 tests in 20.358s
OK (skipped=26)