Update conda-build to remove libarchive-style zstd:compression-level compression tuple

[dholth]

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• I searched open requests and couldn't find a duplicate

What is the idea?

While reading conda-build's source code I noticed

        cph_kwargs["compression_tuple"] = (
            ".tar.zst",
            "zstd",
            f"zstd:compression-level={metadata.config.zstd_compression_level}",
        )

This references a libarchive feature.

Now that conda-package-handling is using python-zstandard, we can set compression without string parsing. We could also allow auto-threads. We would need to require conda-package-handling >=2.

https://github.com/conda/conda-package-handling/blob/main/src/conda_package_handling/conda_fmt.py#L53-L60

Unfortunately the current conda-package-handling API would require us to instantiate a python-zstandard object ourselves, which would be unfortunate if -handling decided to change its preferred compression library.