feat: add tx sign/send and Stellar trait #534

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 45s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 29s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	10m 11s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	19m 7s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	24m 29s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	15m 5s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	17m 0s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	8m 58s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	3h 24m 23s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	22m 50s
	5h 53m 17s

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