Misc fixes/improvements for tx generator. (#4529) #6228

Job	Run time
cargo-deny (advisories)	48s
cargo-deny (bans licenses sources)	44s
rust-check-git-rev-deps	16s
build (gcc, current)	1h 5m 44s
fmt	25s
build (gcc, current, --check-test-tx-meta)	50m 47s
build (gcc, next)	1h 5m 34s
build (gcc, next, --check-test-tx-meta)	52m 11s
build (clang, current)	53m 29s
build (clang, current, --check-test-tx-meta)	43m 26s
build (clang, next)	57m 41s
build (clang, next, --check-test-tx-meta)	42m 50s
complete	1s
	7h 13m 56s

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