feat: add tx sign/send and Stellar trait #764

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	13m 51s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 54s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	10m 16s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	13m 53s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	13m 45s
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)	13m 54s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	9m 43s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	13m 54s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	13m 45s
	2h 10m 47s

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