Improve type hints in saj

[epenet]

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Linked to #87068

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[home-assistant]

Hey there @fredericvl, mind taking a look at this pull request as it has been labeled with an integration (saj) you are listed as a code owner for? Thanks!

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[epenet]

From what I can work out in the pysaj code, the read method returns True, False or raise an exception.
To make it clearer I have renamed the variable.

See https://github.com/fredericvl/pysaj/blob/b7f6a5021471fc32a89cd58067fd7871615547a8/pysaj/__init__.py#L225

The rest is just type hints.