Fix decompression CLI format detection

[Naman1611]

Problem

python -m snappy -d raises:

TypeError: cannot unpack non-iterable function object

This happens because get_decompress_function() now returns a single decompression function, while the CLI still tries to unpack it into method and read_chunk.

Fix

Update the CLI to use the current single-value return API and remove the obsolete start_chunk argument.

Tests

• Added a regression test for get_decompress_function()
• Added a CLI-level regression test for python -m snappy -d
• Existing test suite passes

[martindurant]

We seem to need to update the CI workflows - would you like to handle this?

[Naman1611]

Yes, happy to handle the CI workflow updates. I’ll take a look at the failing workflow and update it as part of this PR.

[Naman1611]

Yes, I believe they address the same CLI issue. I've already fixed the decompression CLI bug in #154, added regression tests, and pushed an additional fix for the failing sdist CI workflow. Could you please take a look at #154? It includes both the CLI fix and the CI workflow correction. Happy to make any further changes if needed.

[martindurant]

The CI runs may not be starting because they need old versions of the OS.