Add _from_json functionality for pybamm.sign #10835

Job	Run time
style	24s
Example notebooks (ubuntu-latest / Python 3.12)	19m 28s
Example scripts (ubuntu-latest / Python 3.12)	13m 49s
Doctests (ubuntu-latest / Python 3.11)	5m 39s
Tests (ubuntu-latest / Python 3.9)	30m 17s
Tests (ubuntu-latest / Python 3.10)	31m 8s
Tests (ubuntu-latest / Python 3.11)	28m 38s
Tests (ubuntu-latest / Python 3.12)	32m 49s
Tests (macos-12 / Python 3.9)	19m 58s
Tests (macos-12 / Python 3.10)	21m 47s
Tests (macos-12 / Python 3.11)	18m 54s
Tests (macos-12 / Python 3.12)	16m 3s
Tests (macos-14 / Python 3.9)	12m 3s
Tests (macos-14 / Python 3.10)	11m 10s
Tests (macos-14 / Python 3.11)	17m 1s
Tests (macos-14 / Python 3.12)	8m 15s
Tests (windows-latest / Python 3.9)	32m 58s
Tests (windows-latest / Python 3.10)	32m 4s
Tests (windows-latest / Python 3.11)	28m 10s
Tests (windows-latest / Python 3.12)	25m 20s
	6h 45m 55s

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