Don't overwrite codec config values when set. (#700)

* Don't overwrite codec config values when set.

A codec doesn't know where it is in the codec pipeline, so it
cannot know whether `array_spec.dtype` should match `codec.dtype`
or not.

* little more

* FIx test

* fix test

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Co-authored-by: Davis Bennett <[email protected]>

Update release notes for 0.15.0 (#691)

Fix default entrypoint handling on older Pythons (#475)

Support Python 3.12 (#471)

* Support Python 3.12

* Ensure `entries.update(...)` recieves a `dict`

On Python 3.12, the existing code did not produce a `dict` that could be
used to update `entries` whereas previous Python versions had. To
workaround this issue, manually create a `dict` that can be used to
update `entries` with a format consistent to what had been seen in
Python versions before 3.12.