feat(rpc)!: Update `Emitter::mempool` to support `evicted_at` #6972

Job	Run time
prepare	4s
Rust fmt	14s
Build & Test (1.84.1, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	2m 22s
Build & Test (1.84.1, true, --all-features)	4m 6s
Check no_std	30s
Build & Test Examples (example_cli)	36s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	3m 36s
Check WASM	1m 25s
Build & Test Examples (example_bitcoind_rpc_polling)	41s
Build & Test (1.63.0, --all-features)	4m 39s
Build & Test Examples (example_electrum)	58s
Rust clippy	55s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	2m 19s
Build & Test Examples (example_esplora)	54s
Build & Test Examples (example_wallet_electrum)	51s
Build & Test (1.75.0, --all-features)	4m 16s
Build & Test Examples (example_wallet_esplora_async)	1m 9s
Build & Test Examples (example_wallet_esplora_blocking)	53s
Build & Test Examples (example_wallet_rpc)	41s
	31m 9s

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