feat: add tx sign/send and Stellar trait #459

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	13m 54s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	15m 46s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	10m 59s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	15m 25s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	22m 10s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	13m 56s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	15m 25s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	8m 37s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	20m 3s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 38s
	2h 36m 53s

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