add `unpin_all_chat_messages` method #698

Job	Run time
rustfmt	15s
Test stable ubuntu-latest --no-default-features	2m 36s
Test stable ubuntu-latest	2m 55s
Test stable ubuntu-latest --all-features	1m 15s
Test stable macos-latest --no-default-features	3m 59s
Test stable macos-latest	5m 11s
Test stable macos-latest --all-features	1m 55s
Test stable windows-latest --no-default-features	5m 2s
Test stable windows-latest	6m 32s
Test stable windows-latest --all-features	3m 9s
Test beta ubuntu-latest --all-features	1m 27s
Test nightly ubuntu-latest --all-features	1m 12s
Release ${{ matrix.triple }}	0s
	35m 28s

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