feat: add txn sign/send and ledger support #262

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	11m 39s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	12m 57s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	21m 36s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	18m 40s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 21s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	11m 12s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 47s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	10m 41s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	14m 53s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	21m 1s
	2h 36m 47s

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