feat: add tx sign/send and Stellar trait #766

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	15m 12s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 24s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	9m 23s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	14m 58s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 16s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 55s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 31s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	11m 25s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	16m 53s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 29s
	2h 36m 26s

Provide feedback