Misc fixes/improvements for tx generator. #6226

Job	Run time
fmt	24s
rust-check-git-rev-deps	17s
build (gcc, current)	1h 4m 53s
cargo-deny (advisories)	46s
build (gcc, current, --check-test-tx-meta)	50m 23s
cargo-deny (bans licenses sources)	45s
build (gcc, next)	1h 5m 22s
build (gcc, next, --check-test-tx-meta)	57m 18s
build (clang, current)	50m 40s
build (clang, current, --check-test-tx-meta)	41m 38s
build (clang, next)	54m 15s
build (clang, next, --check-test-tx-meta)	43m 19s
complete	1s
	7h 10m 1s

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