Add docs, tested examples, and a story for SEP-990 identity assertion… #3137

Job	Run time
checks / docs	42s
checks / pre-commit	50s
checks / test (3.14, locked, ubuntu-latest)	2m 8s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 7s
checks / test (3.14, lowest-direct, windows-latest)	1m 42s
checks / test (3.14, locked, windows-latest)	2m 14s
checks / test (3.13, lowest-direct, windows-latest)	1m 43s
checks / readme-snippets	10s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.13, locked, windows-latest)	1m 37s
checks / test (3.13, locked, ubuntu-latest)	1m 1s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 16s
checks / test (3.10, locked, ubuntu-latest)	1m 15s
checks / test (3.12, locked, windows-latest)	1m 35s
checks / test (3.10, lowest-direct, windows-latest)	1m 36s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 16s
checks / test (3.10, locked, windows-latest)	1m 47s
checks / test (3.11, locked, ubuntu-latest)	1m 10s
checks / test (3.11, lowest-direct, windows-latest)	1m 35s
checks / test (3.11, locked, windows-latest)	1m 38s
checks / test (3.12, locked, ubuntu-latest)	1m 26s
checks / test (3.12, lowest-direct, windows-latest)	1m 52s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 11s
all-green	5s
	31m 59s

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