feat: add tx sign/send and Stellar trait #461

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 11s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	15m 32s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	8m 48s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	15m 30s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 23s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	13m 52s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 2s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	8m 34s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	19m 28s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	21m 42s
	2h 34m 2s

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