Implement ZstdZarrCompressor

[mkitti]

This implements ZstdZarrCompressor which wraps around CodecZstd as a package extension.

Part of the complication of using package extensions is getting a reference to new types defined in the extension. I created a mechanism by which you could specify the compressor as a string, which would then lookup the type from a dictionary.

I'm also wondering if there might be a general way to wrap TranscodingStreams codecs into Zarr compressors.

[coveralls]

Pull Request Test Coverage Report for Build 9654302116

Details

• 27 of 34 (79.41%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 88.316%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Compressors.jl	4	11	36.36%

Files with Coverage Reduction	New Missed Lines	%
src/Compressors.jl	1	83.08%

Totals
Change from base Build 8981180163:	-0.3%
Covered Lines:	839
Relevant Lines:	950

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9655786902

Details

• 25 of 32 (78.13%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.4%) to 88.291%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Compressors.jl	4	11	36.36%

Files with Coverage Reduction	New Missed Lines	%
src/Compressors.jl	1	83.08%

Totals
Change from base Build 8981180163:	-0.4%
Covered Lines:	837
Relevant Lines:	948

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9656097799

Details

• 26 of 32 (81.25%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 88.397%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Compressors.jl	5	11	45.45%

Files with Coverage Reduction	New Missed Lines	%
src/Compressors.jl	1	84.62%

Totals
Change from base Build 8981180163:	-0.3%
Covered Lines:	838
Relevant Lines:	948

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9657292182

Details

• 32 of 32 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 89.135%

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Totals
Change from base Build 8981180163:	0.5%
Covered Lines:	845
Relevant Lines:	948

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💛 - Coveralls

[mkitti]

An alternative to the string lookup for the compressor, would be to just pass in CodecZstd.ZstdCompressor directly, specifically an instance created by CodecZstd.ZstdFrameCompressor(). Via a conversion mechanism, we could wrap that into a Zarr.Compressor.

[nhz2]

This doesn't support multithreaded use IIUC. I think this should be like

Zarr.jl/src/Compressors.jl

Lines 129 to 131 in f436713

	struct ZlibCompressor <: Compressor
	clevel::Int
	end

where the struct only contains the parameters of the codec.

[mkitti]

I initially wrote it like this, but then I was thinking about all the other potential parameters, even if they do not need to be serialized. I think what we should implement is the ability to copy a compessor.

Frankly, I'm somewhat confused about why one actually needs to serialize the compression level into the array metadata. You do not need that information to decompress the data.