Ts-salobj

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Changes:

* Add type annotations and check them with mypy.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6

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Changes:

* `topics.WriteTopic.set`: make NaNs compare equal when deciding if the data has changed.
As a result, `topics.ControllerEvent.set_put` will no longer output a new event
if the only change is to set NaN values to NaN again.
* `TestCsc` assert_arrays/scalars_equal methods: make NaNs compare equal.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6

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Changes:

* Bug fix: test_idl_parser was still expecting the private_host field to be present.
It is now optional.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6

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Changes:

* Pin the versions of astropy and numpy.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6

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Changes:

* Added function `utc_from_tai_unix`.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6

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Changes:

* Make tests/test_salobj_to_either.py compatible with ts_sal 6.
* `DefaultingValidator`: document that defaults are only handled 2 levels deep.

Requirements:

* ts_ddsconfig
* ts_idl 2
* ts_xml 6.2
* IDL files for Test and Script generated by ts_sal 5
* SALPY_Test generated by ts_sal 5 or 6