`TransactionPool` API uses `async_trait` #9104

Job	Run time
preflight / preflight	41s
preflight / ci-versions	59s
build (polkadot-availability-recovery, availability-recovery-regression-bench)	8m 26s
build (polkadot-availability-distribution, availability-distribution-regression-bench)	6m 22s
build (polkadot-node-core-approval-voting, approval-voting-regression-bench)	23m 48s
build (polkadot-statement-distribution, statement-distribution-regression-bench)	5m 15s
publish-benchmarks	0s
	45m 31s

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