backing: improve session buffering for runtime information #5252

Job	Run time
preflight / preflight	37s
preflight / ci-versions	1m 8s
test-frame-ui	46m 25s
test-full-crypto-feature	2m 39s
cargo-check-benches (master)	21m 10s
cargo-check-benches (current)	20m 54s
cargo-check-each-crate (1)	18m 36s
cargo-check-each-crate (2)	19m 12s
test-node-metrics	8m 21s
cargo-check-each-crate (3)	8m 24s
cargo-check-each-crate (4)	16m 49s
cargo-check-each-crate (5)	24m 34s
cargo-check-each-crate (6)	14m 41s
cargo-check-each-crate (7)	29m 52s
cargo-check-all-crate-macos	10m 54s
test-frame-examples-compile-to-wasm	2m 59s
test-deterministic-wasm	6m 27s
check-tracing	2m 24s
check-metadata-hash	6m 13s
node-bench-regression-guard	27s
All test misc tests passed	1s
	4h 22m 47s

Provide feedback