feat: add txn sign/send and ledger support #259

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	11m 26s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 0s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	10m 28s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	15m 15s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 56s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	11m 24s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 0s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	8m 39s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	19m 6s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	18m 51s
	2h 22m 5s

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