Test storage save and load for evohome (#122510)

* test storage save and load

* fix bug exposed by test

* refactor test

* add JSON for test account/location

* create helpers to load JSON

* refactor test

* baseline refactor

* tweak

* update requiremenst

* rationalise code

* remove conditional in test

* refactor test

* mypy fix

* tweak tests

* working test

* working test 4

* working test 5

* add typed dicts

* working dtms

* lint

* fix dtm asserts

* doc strings

* list

* tweak conditional

* tweak test data sets to extend coverage

* leverage conftest.py for subsequent tests

* revert test storage

* revert part two

* rename symbols

* remove anachronism

* stop unwanted DNS lookup

* Clean up type ignores

* Format

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Co-authored-by: Martin Hjelmare <marhje52@gmail.com>