send-transactions: optimize retry pool (#31) #1000

Job	Run time
benchmark (solana-sdk, cargo +$rust_nightly bench -p solana-sdk --features openssl-vendored)	3m 14s
benchmark (solana-runtime, cargo +$rust_nightly bench -p solana-runtime)	1m 32s
benchmark (solana-gossip, cargo +$rust_nightly bench -p solana-gossip)	3m 19s
benchmark (solana-poh, cargo +$rust_nightly bench -p solana-poh)	1m 40s
benchmark (solana-core, cargo +$rust_nightly bench -p solana-core)	6m 5s
benchmark (sbf, make -C programs/sbf all, cargo +$rust_nightly bench --manifest-path programs/sbf...	1m 33s
benchmark (solana-accounts-db, cargo +$rust_nightly bench -p solana-accounts-db --bench accounts_...	13m 59s
	31m 22s

Provide feedback