feat: add txn sign/send and ledger support #422

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	12m 7s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 57s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	11m 41s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	17m 4s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	18m 36s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	11m 52s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 30s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	10m 21s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	18m 19s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	18m 4s
	2h 25m 31s

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