feat: add txn sign/send and ledger support #428

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	12m 1s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 41s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	9m 49s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	19m 3s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	18m 46s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	12m 11s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	13m 41s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	9m 3s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	16m 24s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 1s
	2h 24m 40s

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