feat: add tx sign/send and Stellar trait #530

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	15m 2s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 56s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	12m 38s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	20m 18s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	22m 55s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 17s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 46s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	12m 30s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	18m 21s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	21m 36s
	2h 51m 19s

Provide feedback