database: add `NostrDatabaseExt::contacts` method #1129

Job	Run time
Build no_std (nightly)	1m 30s
Build FFI (stable, -p nostr-ffi)	5m 16s
Build (stable, -p nostr)	1m 8s
Build FFI (stable, -p nostr-sdk-ffi)	1m 29s
Build (stable, -p nostr-sdk --features rocksdb)	17m 58s
Build (stable, -p nostr --no-default-features --features alloc)	15s
Build WASM (stable, -p nostr)	25s
Build (1.66.0, -p nostr-sdk --features rocksdb)	1m 51s
Build (stable, -p nostr --no-default-features --features "alloc all-nips")	50s
Build WASM (stable, -p nostr-sdk)	1m 5s
Format	7s
Build (stable, -p nostr --features blocking)	2m 3s
Build WASM (stable, -p nostr-sdk --features indexeddb)	59s
Build WASM (stable, -p nostr-js)	46s
Build (stable, -p nostr-database -p nostr-sdk)	3m 9s
Build WASM (1.64.0, -p nostr)	6m 29s
Build (stable, -p nostr-sdk --no-default-features)	1m 9s
Build WASM (1.64.0, -p nostr-sdk)	4m 46s
Build (stable, -p nostr-sdk --features blocking)	1m 44s
Build WASM (1.64.0, -p nostr-sdk --features indexeddb)	4m 54s
Build (stable, -p nostr-sdk --features sqlite)	1m 57s
Build WASM (1.64.0, -p nostr-js)	7m 5s
Build (1.64.0, -p nostr)	7m 51s
Build (1.64.0, -p nostr --no-default-features --features alloc)	4m 37s
Build (1.64.0, -p nostr --no-default-features --features "alloc all-nips")	5m 26s
Build (1.64.0, -p nostr --features blocking)	6m 27s
Build (1.64.0, -p nostr-database -p nostr-sdk)	5m 49s
Build (1.64.0, -p nostr-sdk --no-default-features)	7m 31s
Build (1.64.0, -p nostr-sdk --features blocking)	5m 47s
Build (1.64.0, -p nostr-sdk --features sqlite)	6m 18s
	1h 56m 41s

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