Misc fixes/improvements for tx generator. #6200

Job	Run time
fmt	23s
rust-check-git-rev-deps	18s
cargo-deny (advisories)	44s
build (gcc, current)	45m 45s
cargo-deny (bans licenses sources)	46s
build (gcc, current, --check-test-tx-meta)	50m 35s
build (gcc, next)	48m 16s
build (gcc, next, --check-test-tx-meta)	50m 8s
build (clang, current)	51m 45s
build (clang, current, --check-test-tx-meta)	42m 16s
build (clang, next)	50m 22s
build (clang, next, --check-test-tx-meta)	43m 58s
complete	1s
	6h 25m 17s

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