Tests

Lazy-load chat histories, fast list summaries, and mtime disk cache (closes #84) #164

Job	Run time
Typecheck (mypy)	17s
Unit tests (macos-latest / Python 3.13)	21s
Secret scan (gitleaks)	4s
Unit tests (macos-latest / Python 3.10)	35s
Unit tests (windows-latest / Python 3.10)	1m 39s
Unit tests (windows-latest / Python 3.11)	1m 1s
Unit tests (windows-latest / Python 3.12)	1m 27s
Unit tests (macos-latest / Python 3.11)	21s
Unit tests (windows-latest / Python 3.13)	54s
Unit tests (ubuntu-latest / Python 3.13)	26s
Unit tests (ubuntu-latest / Python 3.12)	28s
Unit tests (macos-latest / Python 3.12)	16s
Unit tests (ubuntu-latest / Python 3.10)	27s
Lock file freshness	8s
Unit tests (ubuntu-latest / Python 3.11)	24s
	8m 48s

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