improve offline tx handling #534

Job	Run time
build-binaries	10m 29s
build-wasm (wasm, build-wasm-scripts, wasm/tx_.wasm wasm/vp_.wasm wasm/checksums.json )	4m 20s
changelog	0s
build-wasm (wasm-for-tests, build-wasm-tests-scripts, wasm_for_tests/*.wasm)	3m 38s
check-packages	6m 14s
lints	5m 56s
rust-docs	6m 49s
test-wasm	5m 10s
test-unit	11m 32s
test-integration	13m 32s
check-benchmarks	0s
test-e2e	0s
	1h 7m 40s

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