feat: implement scale-offset and data type casting via codecs

[d-v-b]

this PR defines the scale-offset transformation as a pair of codecs: a ScaleOffset codec, which implements the Zarr V3 scale-offset codec , and the CastValueRustV1 codec from cast-value.py, which implements the Zarr V3 cast_value codec. This means float data can be decoded as float, but stored as ints, in a cf- and xarray-independent manner.

Right now it's exposed via a boolean parameter to convert_s2_optimized, and command-line flag --experimental-scale-offset-codec.

caveat: downstream consumers will need the ScaleOffset and CastValue codecs available in order to decode the data. We should work on ways to make this straightforward.

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Codecov Report

❌ Patch coverage is 90.62500% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/eopf_geozarr/codecs/scale_offset.py	87.23%	6 Missing ⚠️

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[d-v-b]

I did not make a stand-alone library for this codec, because it is so simple.

[emmanuelmathot]

ok but will it live in zarr-python or will users have to import eopf-geozarr to use the scale_offset?

[d-v-b]

in the current state users have to import eopf-geozarr, but I don't like that outcome. I will see if we can get this into zarr-python